Network Working Group P. Saint-Andre
Internet-Draft J. Miller
Expires: April 25, 2004 Jabber Software Foundation
October 26, 2003
XMPP Instant Messaging
draft-ietf-xmpp-im-18
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at http://
www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 25, 2004.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This memo describes extensions to and applications of the core
features of the Extensible Messaging and Presence Protocol (XMPP Core
[1]) that provide the basic instant messaging (IM) and presence
functionality defined in RFC 2779 [2].
Saint-Andre & Miller Expires April 25, 2004 [Page 1]
Internet-Draft XMPP Instant Messaging October 2003
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 6
1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
1.4 Discussion Venue . . . . . . . . . . . . . . . . . . . . . 7
1.5 Intellectual Property Notice . . . . . . . . . . . . . . . 7
2. Syntax of XML Stanzas . . . . . . . . . . . . . . . . . . 7
2.1 Message Syntax . . . . . . . . . . . . . . . . . . . . . . 7
2.1.1 Types of Message . . . . . . . . . . . . . . . . . . . . . 7
2.1.2 Child Elements . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Presence Syntax . . . . . . . . . . . . . . . . . . . . . 10
2.2.1 Types of Presence . . . . . . . . . . . . . . . . . . . . 10
2.2.2 Child Elements . . . . . . . . . . . . . . . . . . . . . . 11
2.3 IQ Syntax . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4 Extended Namespaces . . . . . . . . . . . . . . . . . . . 12
3. Session Establishment . . . . . . . . . . . . . . . . . . 13
4. Exchanging Messages . . . . . . . . . . . . . . . . . . . 16
4.1 Specifying an Intended Recipient . . . . . . . . . . . . . 16
4.2 Specifying a Message Type . . . . . . . . . . . . . . . . 17
4.3 Specifying a Message Body . . . . . . . . . . . . . . . . 17
4.4 Specifying a Message Subject . . . . . . . . . . . . . . . 17
4.5 Specifying a Conversation Thread . . . . . . . . . . . . . 18
5. Exchanging Presence Information . . . . . . . . . . . . . 19
5.1 Client and Server Presence Responsibilities . . . . . . . 19
5.2 Specifying Availability Status . . . . . . . . . . . . . . 22
5.3 Specifying Detailed Status Information . . . . . . . . . . 22
5.4 Specifying Presence Priority . . . . . . . . . . . . . . . 22
5.5 Presence Examples . . . . . . . . . . . . . . . . . . . . 22
6. Managing Subscriptions . . . . . . . . . . . . . . . . . . 26
6.1 Requesting a Subscription . . . . . . . . . . . . . . . . 26
6.2 Handling a Subscription Request . . . . . . . . . . . . . 27
6.3 Cancelling a Subscription from Another Entity . . . . . . 27
6.4 Unsubscribing from Another Entity's Presence . . . . . . . 27
7. Roster Management . . . . . . . . . . . . . . . . . . . . 28
7.1 Syntax and Semantics . . . . . . . . . . . . . . . . . . . 28
7.2 Business Rules . . . . . . . . . . . . . . . . . . . . . . 29
7.3 Retrieving One's Roster on Login . . . . . . . . . . . . . 29
7.4 Adding a Roster Item . . . . . . . . . . . . . . . . . . . 30
7.5 Updating a Roster Item . . . . . . . . . . . . . . . . . . 31
7.6 Deleting a Roster Item . . . . . . . . . . . . . . . . . . 31
8. Integration of Roster Items and Presence Subscriptions . . 32
8.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 32
8.2 User Subscribes to Contact . . . . . . . . . . . . . . . . 33
8.2.1 Alternate Flow: Contact Declines Subscription Request . . 37
8.3 Creating a Mutual Subscription . . . . . . . . . . . . . . 38
8.3.1 Alternate Flow: User Declines Subscription Request . . . . 41
Saint-Andre & Miller Expires April 25, 2004 [Page 2]
Internet-Draft XMPP Instant Messaging October 2003
8.4 Unsubscribing . . . . . . . . . . . . . . . . . . . . . . 43
8.4.1 Case #1: Unsubscribing When Subscription is Not Mutual . . 43
8.4.2 Case #2: Unsubscribing When Subscription is Mutual . . . . 45
8.5 Cancelling a Subscription . . . . . . . . . . . . . . . . 48
8.5.1 Case #1: Cancelling When Subscription is Not Mutual . . . 48
8.5.2 Case #2: Cancelling When Subscription is Mutual . . . . . 50
8.6 Removing a Roster Item and Cancelling All Subscriptions . 52
9. Subscription States . . . . . . . . . . . . . . . . . . . 54
9.1 Defined States . . . . . . . . . . . . . . . . . . . . . . 54
9.2 Server Handling of Outbound Presence, Categorized by
Subscription State . . . . . . . . . . . . . . . . . . . . 55
9.2.1 Subscription State = None . . . . . . . . . . . . . . . . 55
9.2.2 Subscription State = None + Pending Out . . . . . . . . . 55
9.2.3 Subscription State = None + Pending In . . . . . . . . . . 56
9.2.4 Subscription State = None + Pending Out/In . . . . . . . . 56
9.2.5 Subscription State = To . . . . . . . . . . . . . . . . . 56
9.2.6 Subscription State = To + Pending In . . . . . . . . . . . 56
9.2.7 Subscription State = From . . . . . . . . . . . . . . . . 57
9.2.8 Subscription State = From + Pending Out . . . . . . . . . 57
9.2.9 Subscription State = Both . . . . . . . . . . . . . . . . 57
9.3 Server Handling of Outbound Presence, Categorized by
Presence Type . . . . . . . . . . . . . . . . . . . . . . 57
9.3.1 Subscribe . . . . . . . . . . . . . . . . . . . . . . . . 58
9.3.2 Subscribed . . . . . . . . . . . . . . . . . . . . . . . . 58
9.3.3 Unsubscribe . . . . . . . . . . . . . . . . . . . . . . . 58
9.3.4 Unsubscribed . . . . . . . . . . . . . . . . . . . . . . . 59
9.4 Server Handling of Inbound Presence, Categorized by
Subscription State . . . . . . . . . . . . . . . . . . . . 59
9.4.1 Subscription State = None . . . . . . . . . . . . . . . . 59
9.4.2 Subscription State = None + Pending Out . . . . . . . . . 60
9.4.3 Subscription State = None + Pending In . . . . . . . . . . 60
9.4.4 Subscription State = None + Pending Out/In . . . . . . . . 60
9.4.5 Subscription State = To . . . . . . . . . . . . . . . . . 60
9.4.6 Subscription State = To + Pending In . . . . . . . . . . . 61
9.4.7 Subscription State = From . . . . . . . . . . . . . . . . 61
9.4.8 Subscription State = From + Pending Out . . . . . . . . . 61
9.4.9 Subscription State = Both . . . . . . . . . . . . . . . . 61
9.5 Server Handling of Inbound Presence, Categorized by
Presence Type . . . . . . . . . . . . . . . . . . . . . . 62
9.5.1 Subscribe . . . . . . . . . . . . . . . . . . . . . . . . 62
9.5.2 Subscribed . . . . . . . . . . . . . . . . . . . . . . . . 62
9.5.3 Unsubscribe . . . . . . . . . . . . . . . . . . . . . . . 62
9.5.4 Unsubscribed . . . . . . . . . . . . . . . . . . . . . . . 63
9.6 Server Delivery and Client Acknowledgement of
Subscription State Change Notifications . . . . . . . . . 63
10. Blocking Communication . . . . . . . . . . . . . . . . . . 64
10.1 Syntax and Semantics . . . . . . . . . . . . . . . . . . . 65
10.2 Business Rules . . . . . . . . . . . . . . . . . . . . . . 67
Saint-Andre & Miller Expires April 25, 2004 [Page 3]
Internet-Draft XMPP Instant Messaging October 2003
10.3 Retrieving One's Privacy Lists . . . . . . . . . . . . . . 68
10.4 Managing Active Lists . . . . . . . . . . . . . . . . . . 70
10.5 Managing the Default List . . . . . . . . . . . . . . . . 72
10.6 Editing a Privacy List . . . . . . . . . . . . . . . . . . 73
10.7 Adding a New Privacy List . . . . . . . . . . . . . . . . 73
10.8 Removing a Privacy List . . . . . . . . . . . . . . . . . 73
10.9 Blocking Messages . . . . . . . . . . . . . . . . . . . . 74
10.10 Blocking Inbound Presence Notifications . . . . . . . . . 76
10.11 Blocking Outbound Presence Notifications . . . . . . . . . 78
10.12 Blocking IQs . . . . . . . . . . . . . . . . . . . . . . . 79
10.13 Blocking All Communication . . . . . . . . . . . . . . . . 81
10.14 Blocked Entity Attempts to Communicate with User . . . . . 82
10.15 Higher-Level Heuristics . . . . . . . . . . . . . . . . . 83
11. IANA Considerations . . . . . . . . . . . . . . . . . . . 84
11.1 XML Namespace Name for Session Data . . . . . . . . . . . 84
12. Internationalization Considerations . . . . . . . . . . . 84
13. Security Considerations . . . . . . . . . . . . . . . . . 85
14. Server Rules for Handling XML Stanzas . . . . . . . . . . 85
15. Compliance Requirements . . . . . . . . . . . . . . . . . 87
15.1 Servers . . . . . . . . . . . . . . . . . . . . . . . . . 87
15.2 Clients . . . . . . . . . . . . . . . . . . . . . . . . . 87
Normative References . . . . . . . . . . . . . . . . . . . 88
Informative References . . . . . . . . . . . . . . . . . . 88
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 89
A. vCards . . . . . . . . . . . . . . . . . . . . . . . . . . 89
B. XML Schemas . . . . . . . . . . . . . . . . . . . . . . . 89
B.1 jabber:client . . . . . . . . . . . . . . . . . . . . . . 89
B.2 jabber:server . . . . . . . . . . . . . . . . . . . . . . 93
B.3 session . . . . . . . . . . . . . . . . . . . . . . . . . 97
B.4 jabber:iq:privacy . . . . . . . . . . . . . . . . . . . . 98
B.5 jabber:iq:roster . . . . . . . . . . . . . . . . . . . . . 100
C. Differences Between Jabber Instant Messaging and XMPP . . 101
C.1 Session Creation . . . . . . . . . . . . . . . . . . . . . 101
C.2 Privacy Rules . . . . . . . . . . . . . . . . . . . . . . 102
D. Revision History . . . . . . . . . . . . . . . . . . . . . 102
D.1 Changes from draft-ietf-xmpp-im-17 . . . . . . . . . . . . 102
D.2 Changes from draft-ietf-xmpp-im-16 . . . . . . . . . . . . 102
D.3 Changes from draft-ietf-xmpp-im-15 . . . . . . . . . . . . 103
D.4 Changes from draft-ietf-xmpp-im-14 . . . . . . . . . . . . 103
D.5 Changes from draft-ietf-xmpp-im-13 . . . . . . . . . . . . 103
D.6 Changes from draft-ietf-xmpp-im-12 . . . . . . . . . . . . 104
D.7 Changes from draft-ietf-xmpp-im-11 . . . . . . . . . . . . 104
D.8 Changes from draft-ietf-xmpp-im-10 . . . . . . . . . . . . 104
D.9 Changes from draft-ietf-xmpp-im-09 . . . . . . . . . . . . 105
D.10 Changes from draft-ietf-xmpp-im-08 . . . . . . . . . . . . 105
D.11 Changes from draft-ietf-xmpp-im-07 . . . . . . . . . . . . 105
D.12 Changes from draft-ietf-xmpp-im-06 . . . . . . . . . . . . 105
D.13 Changes from draft-ietf-xmpp-im-05 . . . . . . . . . . . . 105
Saint-Andre & Miller Expires April 25, 2004 [Page 4]
Internet-Draft XMPP Instant Messaging October 2003
D.14 Changes from draft-ietf-xmpp-im-04 . . . . . . . . . . . . 106
D.15 Changes from draft-ietf-xmpp-im-03 . . . . . . . . . . . . 106
D.16 Changes from draft-ietf-xmpp-im-02 . . . . . . . . . . . . 106
D.17 Changes from draft-ietf-xmpp-im-01 . . . . . . . . . . . . 106
D.18 Changes from draft-ietf-xmpp-im-00 . . . . . . . . . . . . 107
D.19 Changes from draft-miller-xmpp-im-02 . . . . . . . . . . . 107
Intellectual Property and Copyright Statements . . . . . . 108
Saint-Andre & Miller Expires April 25, 2004 [Page 5]
Internet-Draft XMPP Instant Messaging October 2003
1. Introduction
1.1 Overview
The Extensible Messaging and Presence Protocol (XMPP) is a protocol
for streaming XML [3] elements in order to exchange messages and
presence information in close to real time. The core features of XMPP
are defined in XMPP Core [1]. These features -- specifically XML
streams, stream authentication and encryption, and the <message/>,
<presence/>, and <iq/> children of the stream root -- 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 [4]. This memo describes
extensions to and applications of the core features of XMPP that
provide the basic functionality expected of an instant messaging (IM)
and presence application as defined in RFC 2779 [2].
1.2 Requirements
For the purposes of this memo, the requirements of a basic instant
messaging and presence application are defined by RFC 2779 [2]. At a
high level, RFC 2779 stipulates that a user must be able to complete
the following use cases:
o Exchange messages with other users
o Exchange presence information with other users
o Manage subscriptions to and from other users
o Manage items in a contact list (in XMPP this is called a "roster")
o Block communications to or from specific other users
Detailed definitions of these functionality areas are contained in
RFC 2779, and the interested reader is directed to that document
regarding the requirements addressed herein.
Note: while XMPP-based instant messaging and presence meets the
requirements of RFC 2779, it was not designed explicitly with RFC
2779 in mind, since the base protocol evolved through an open
development process within the Jabber open-source community before
RFC 2779 was written. Note also that although protocols addressing
many other functionality areas have been defined in the Jabber
community, such protocols are not included in this memo because they
are not required by RFC 2779 [2].
Saint-Andre & Miller Expires April 25, 2004 [Page 6]
Internet-Draft XMPP Instant Messaging October 2003
1.3 Terminology
This memo inherits the terminology defined in XMPP Core [1].
The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [5].
1.4 Discussion Venue
The authors welcome discussion and comments related to the topics
presented in this document. The preferred forum is the
<xmppwg@jabber.org> mailing list, for which archives and subscription
information are available at <http://www.jabber.org/cgi-bin/mailman/
listinfo/xmppwg/>.
1.5 Intellectual Property Notice
This document is in full compliance with all provisions of Section 10
of RFC 2026. Parts of this specification use the term "jabber" for
identifying namespaces and other protocol syntax. Jabber[tm] is a
registered trademark of Jabber, Inc. Jabber, Inc. grants permission
to the IETF for use of the Jabber trademark in association with this
specification and its successors, if any.
2. Syntax of XML Stanzas
The basic semantics and common attributes of XML stanzas qualified by
the 'jabber:client' and 'jabber:server' namespaces are defined in
XMPP Core [1]. However, these namespaces also define various child
elements, as well as values for the common 'type' attribute, that are
specific to instant messaging and presence applications. Thus, before
addressing particular "use cases" for such applications, we here
further describe the syntax of XML stanzas, thereby supplementing the
discussion in XMPP Core [1].
2.1 Message Syntax
Message stanzas in the 'jabber:client' or 'jabber:server' namespace
are used to "push" information to another entity. Common uses 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 errors.
2.1.1 Types of Message
The 'type' attribute of a message stanza is RECOMMENDED; if included,
Saint-Andre & Miller Expires April 25, 2004 [Page 7]
Internet-Draft XMPP Instant Messaging October 2003
it specifies the conversational context of the message, thus
providing a hint regarding presentation (e.g., in a GUI). If
included, the 'type' attribute MUST have one of the following values:
o chat -- The message is sent in the context of a one-to-one chat
conversation. A compliant client SHOULD present the message an
interface enabling one-to-one chat between the two parties,
including an appropriate conversation history.
o error -- An error has occurred related to a previous message sent
by the sender (for details regarding stanza error syntax, refer to
XMPP Core [1]). A compliant client 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. A compliant client SHOULD present the message 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 memo.
o headline -- The message is probably generated by an automated
service that delivers or broadcasts content (news, sports, market
information, RSS feeds, etc.). No reply to the message is
expected, and a compliant client SHOULD present the message 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).
o normal -- The message is a single 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 compliant client
SHOULD present the message in an interface enabling the recipient
to reply.
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). The "error" type MUST be generated only in
response to an error related to a message received from another
entity.
Although the 'type' attribute is NOT REQUIRED, 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').
Saint-Andre & Miller Expires April 25, 2004 [Page 8]
Internet-Draft XMPP Instant Messaging October 2003
2.1.2 Child Elements
As described under extended namespaces (Section 2.4), a message
stanza MAY contain any properly-namespaced child element.
In accordance with the default namespace declaration, by default a
message stanza is in the 'jabber:client' or 'jabber:server'
namespace, which defines certain allowable children of message
stanzas. If the message stanza is of type "error", it MUST include an
<error/> child; for details, see XMPP Core [1]. Otherwise, the
message stanza MAY contain any of the following child elements
without an explicit namespace declaration:
1. <subject/>
2. <body/>
3. <thread/>
2.1.2.1 Subject
The <subject/> element contains XML character data that specifies the
topic of the message. The <subject/> element MUST NOT possess any
attributes, with the exception of the 'xml:lang' attribute. Multiple
instances of the <subject/> element MAY be included for the purpose
of providing alternate versions of the same subject, but only if each
instance possesses an 'xml:lang' attribute with a distinct language
value. The <subject/> element MUST NOT contain mixed content (as
defined in Section 3.2.2 of the XML specification [3]).
2.1.2.2 Body
The <body/> element contains XML character data that specifies the
textual contents of the message; this child element is normally
included but NOT REQUIRED. The <body/> element MUST NOT possess any
attributes, with the exception of the 'xml:lang' attribute. Multiple
instances of the <body/> element MAY be included but only if each
instance possesses an 'xml:lang' attribute with a distinct language
value. The <body/> element MUST NOT contain mixed content (as defined
in Section 3.2.2 of the XML specification [3]).
2.1.2.3 Thread
The <thread/> element contains XML character data that specifies an
identifier that is used for tracking a conversation thread (sometimes
referred to as an "instant messaging session") between two entities.
The value of the <thread/> element is generated by the sender and
Saint-Andre & Miller Expires April 25, 2004 [Page 9]
Internet-Draft XMPP Instant Messaging October 2003
that SHOULD be copied back in any replies. If used, it MUST be unique
to that conversation thread within the stream and MUST be consistent
throughout that conversation (a client that receives a message from
the same full JID but with a different thread ID MUST assume that the
message in question exists outside the context of the existing
conversation thread). The use of the <thread/> element is OPTIONAL
and is not used to identify individual messages, only conversations.
A message stanza MUST NOT contain more than one <thread/> element.
The <thread/> element MUST NOT possess any attributes. The value of
the <thread/> element 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 <thread/> element MUST NOT contain mixed
content (as defined in Section 3.2.2 of the XML specification [3]).
2.2 Presence Syntax
Presence stanzas are used in the 'jabber:client' or 'jabber:server'
namespace to express an entity's current availability status (offline
or online, along with various sub-states of the latter and optional
user-defined descriptive text), and to communicate that status to
other entities. Presence stanzas are also used to negotiate and
manage subscriptions to the presence of other entities.
2.2.1 Types of Presence
The 'type' attribute of a presence stanza is OPTIONAL. A presence
stanza that does not possess a 'type' attribute is used to signal to
the server that the sender is online and available for communication.
If included, the 'type' attribute specifies a lack of availability, a
request to manage a subscription to another entity's presence, a
request for another entity's current presence, or an error related to
a previously-sent presence stanza. If included, the 'type' attribute
MUST have one of the following values:
o unavailable -- Signals that the entity is no longer available for
communication.
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 -- A notification that an entity is unsubscribing from
another entity's presence.
o unsubscribed -- The subscription request has been denied or a
previously-granted subscription has been cancelled.
Saint-Andre & Miller Expires April 25, 2004 [Page 10]
Internet-Draft XMPP Instant Messaging October 2003
o probe -- A request for an entity's current presence; SHOULD be
generated only by a server and SHOULD NOT be generated by a
client.
o error -- An error has occurred regarding processing or delivery of
a previously-sent presence stanza.
For detailed information regarding presence semantics and the
subscription model used in the context of XMPP-based instant
messaging and presence applications, refer to Exchanging Presence
Information (Section 5) and Managing Subscriptions (Section 6).
2.2.2 Child Elements
As described under extended namespaces (Section 2.4), a presence
stanza MAY contain any properly-namespaced child element.
In accordance with the default namespace declaration, by default a
presence stanza is in the 'jabber:client' or 'jabber:server'
namespace, which defines certain allowable children of presence
stanzas. If the presence stanza is of type "error", it MUST include
an <error/> child; for details, see XMPP Core [1]. If the presence
stanza possesses no 'type' attribute, it MAY contain any of the
following child elements (note that the <status/> child MAY be sent
in a presence stanza of type "unavailable" or, for historical
reasons, "subscribe"):
1. <show/>
2. <status/>
3. <priority/>
2.2.2.1 Show
The OPTIONAL <show/> element contains XML character data that
specifies the particular availability status of an entity or specific
resource. A presence stanza MUST NOT contain more than one <show/>
element. The <show/> element MUST NOT possess any attributes. The XML
character data contained in the <show/> element is not intended to be
human-readable. If provided, the CDATA value MUST be one of the
following (additional availability types 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.
Saint-Andre & Miller Expires April 25, 2004 [Page 11]
Internet-Draft XMPP Instant Messaging October 2003
o xa -- The entity or resource is away for an extended period (xa =
"eXtended Away").
o dnd -- The entity or resource is busy (dnd = "Do Not Disturb").
If no <show/> element is provided, the entity is assumed to be online
and available.
2.2.2.2 Status
The OPTIONAL <status/> element contains a natural-language
description of availability status. It is normally used in
conjunction with the show element to provide a detailed description
of an availability state (e.g., "In a meeting"). The <status/>
element MUST NOT possess any attributes, with the exception of the
'xml:lang' attribute. Multiple instances of the <status/> element MAY
be included but only if each instance possesses an 'xml:lang'
attribute with a distinct language value.
2.2.2.3 Priority
The OPTIONAL <priority/> element contains XML character data that
specifies the priority level of the connected resource. The value may
be any integer between -128 and +127. A presence stanza MUST NOT
contain more than one <priority/> element. The <priority/> element
MUST NOT possess any attributes. If no priority is provided, a server
SHOULD consider the priority to be zero. For information regarding
the semantics of priority values in stanza routing within instant
messaging and presence applications, refer to Server Rules for
Handling XML Stanzas (Section 14).
2.3 IQ Syntax
IQ stanzas provide a structured request-response mechanism. The basic
semantics of that mechanism are defined in XMPP Core [1], whereas the
specific semantics required to complete particular use cases are
defined in all cases by an extended namespace (Section 2.4) (note
that the 'jabber:client' and 'jabber:server' namespaces do not define
any children of IQ stanzas). This memo defines two such extended
namespaces, one for Roster Management (Section 7) and the other for
Blocking Communication (Section 10); however, an IQ stanza MAY
contain structured information qualified by any extended namespace.
2.4 Extended Namespaces
While the three XML stanza kinds defined in the "jabber:client" or
"jabber:server" namespace (along with their attributes and child
elements) provide a basic level of functionality for messaging and
Saint-Andre & Miller Expires April 25, 2004 [Page 12]
Internet-Draft XMPP Instant Messaging October 2003
presence, XMPP uses XML namespaces to extend the stanzas for the
purpose of providing additional functionality. Thus a message or
presence MAY contain one or more optional child elements containing
content that extends the meaning of the message (e.g., an
XHTML-formatted version of the message body), and an IQ stanza MAY
contain one such child element. This child element MAY have any name
and MUST possess an 'xmlns' namespace declaration (other than
"jabber:client", "jabber:server", or "http://etherx.jabber.org/
streams") that defines all data contained within the child element.
Support for any given extended namespace is OPTIONAL on the part of
any implementation (aside from the extended namespaces defined
herein). If an entity does not understand such a namespace, the
entity's expected behavior depends on whether the entity is (1) the
recipient or (2) an entity that is routing the stanza to the
recipient:
Recipient: If a recipient receives a stanza that contains a child
element it does not understand, it SHOULD ignore that specific XML
data, i.e., it SHOULD not process it or present it to a user or
associated application (if any). In particular:
* If an entity receives a message or presence stanza that
contains XML data qualified by a namespace it does not
understand, the portion of the stanza that is in the unknown
namespace SHOULD be ignored.
* If an entity receives a message stanza whose only child element
is qualified by a namespace it does not understand, it MUST
ignore the entire stanza.
* If an entity receives an IQ stanza of type "get" or "set"
containing a child element qualified by a namespace it does not
understand, the entity SHOULD return an IQ stanza of type
"error" with an error condition of <feature-not-implemented/>.
Router: If a routing entity (usually a server) handles a stanza that
contains a child element it does not understand, it SHOULD ignore
the associated XML data by passing it on untouched to the
recipient.
3. Session Establishment
Most instant messaging and presence applications based on XMPP are
implemented via a client-server architecture that requires a client
to establish a session on a server in order to engage in the expected
instant messaging and presence activities. However, there are several
Saint-Andre & Miller Expires April 25, 2004 [Page 13]
Internet-Draft XMPP Instant Messaging October 2003
pre-conditions that MUST be met before a client can establish an
instant messaging and presence session. These are:
1. Stream Authentication -- a client MUST complete stream
authentication as documented in XMPP Core [1] before attempting
to establish a session or send any XML stanzas.
2. Resource Binding -- after completing stream authentication, a
client MUST bind a resource to the stream so that the client's
address is of the form <user@domain/resource>.
If a server supports sessions, it MUST include a <session/> element
qualified by the 'urn:ietf:params:xml:ns:xmpp-session' namespace in
the stream features it advertises to a client after the completion of
stream authentication as defined in XMPP Core [1]:
Server advertises session establishment feature to client:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='c2s_345'
from='example.com'
version='1.0'>
<stream:features>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<session xmlns='urn:ietf:params:xml:ns:xmpp-session'>
</stream:features>
Upon being so informed that session establishment is required (and
after completing resource binding), the client SHOULD establish a
session by sending to the server an IQ stanza of type "set"
containing an empty <session/> child element qualified by the
'urn:ietf:params:xml:ns:xmpp-session' namespace:
Step 1: Client requests session with server:
<iq from='someuser@example.com'
to='example.com'
type='set'
id='sess_1'>
<session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
</iq>
Step 2: Server informs client that session has been created:
<iq from='example.com'
to='someuser@example.com'
Saint-Andre & Miller Expires April 25, 2004 [Page 14]
Internet-Draft XMPP Instant Messaging October 2003
type='result'
id='sess_1'/>
Several error conditions are possible. For example, the server may
encounter an internal condition that prevents it from creating the
session, the username or authorization identity may lack permissions
to create a session, or there may already be an active session
associated with a resource of the same name.
If the server encounters an internal condition that prevents it from
creating the session, it MUST return an error.
Step 2 (alt): Server responds with error (internal server error):
<iq type='error' id='sess_1'>
<session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
<error type='wait'>
<internal-server-error
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
If the username or resource is not allowed to create a session, the
server MUST return an error (e.g., forbidden).
Step 2 (alt): Server responds with error (username or resource not
allowed to create session):
<iq type='error' id='sess_1'>
<session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
<error type='auth'>
<forbidden
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
If there is already an active session of the same name, the server
MUST either (1) terminate the active session and allow the
newly-requested session, or (2) disallow the newly-requested session
and maintain the existing session. Which of these the server does is
up to the implementation, although it is RECOMMENDED to implement
case #1. In case #1, the server SHOULD send a <conflict/> stream
error to the active session; in case #2, the server SHOULD send a
<conflict/> stanza error to the newly-requested session.
Step 2 (alt): Server informs active session of resource conflict
(case #1):
Saint-Andre & Miller Expires April 25, 2004 [Page 15]
Internet-Draft XMPP Instant Messaging October 2003
<stream:error>
<conflict xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
Step 2 (alt): Server informs newly-requested session of resource
conflict (case #2):
<iq type='error' id='sess_1'>
<session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
<error type='cancel'>
<conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
After establishing a session, a client SHOULD send initial presence
and request its roster as described below, although these actions are
NOT REQUIRED.
Note: before allowing the creation of instant messaging and presence
sessions, a server MAY require prior account provisioning. Possible
methods for account provisioning include account creation by a server
administrator as well as in-band account registration using the
'jabber:iq:register' namespace; the latter method is documented by
the Jabber Software Foundation [7] at <http://www.jabber.org/
protocol/> but is out of scope for this memo.
4. Exchanging Messages
Exchanging messages is a basic use of XMPP and is brought about when
a user generates a message stanza that is addressed to another
entity. As defined under Server Rules for Handling XML Stanzas
(Section 14), 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).
For information regarding the syntax of message stanzas as well as
their defined attributes and child elements, refer to Message Syntax
(Section 2.1).
4.1 Specifying an Intended Recipient
An instant messaging client SHOULD specify an intended recipient for
a message by providing the JID of an entity other than the sender in
the 'to' attribute of the <message/> stanza. If the message is being
sent in reply to a message previously received from an address of the
form <user@domain/resource> (e.g., within the context of a chat
Saint-Andre & Miller Expires April 25, 2004 [Page 16]
Internet-Draft XMPP Instant Messaging October 2003
session), the value of the 'to' address SHOULD be the full JID
(<user@domain/resource>) rather than merely <user@domain> unless the
sender has knowledge (via presence) that the intended recipient's
resource is no longer available. If the message is being sent outside
the context of any existing chat session or received message, the
value of the 'to' address SHOULD be of the form <user@domain> rather
than <user@domain/resource>.
4.2 Specifying a Message Type
As noted, it is RECOMMENDED for a message stanza to possess a 'type'
attribute whose value captures the conversational context (if any) of
the message (see Type (Section 2.1.1)).
The following example shows a valid value of the 'type' attribute:
Example: A message of a defined type:
<message
to='romeo@example.net'
from='juliet@example.com/balcony'
type='chat'
xml:lang='en'>
<body>Wherefore art thou, Romeo?</body>
</message>
4.3 Specifying a Message Body
A message stanza MAY (and often will) contain a child <body/> element
whose XML character data specifies the primary meaning of the message
(see Body (Section 2.1.2.2)).
Example: A message with a body:
<message
to='romeo@example.net'
from='juliet@example.com/balcony'
type='chat'
xml:lang='en'>
<body>Wherefore art thou, Romeo?</body>
<body xml:lang='cz'>PročeŽ jsi ty, Romeo?</body>
</message>
4.4 Specifying a Message Subject
A message stanza MAY contain one or more child <subject/> elements
Saint-Andre & Miller Expires April 25, 2004 [Page 17]
Internet-Draft XMPP Instant Messaging October 2003
specifying the topic of the message (see Subject (Section 2.1.2.1)).
Example: A message with a subject:
<message
to='romeo@example.net'
from='juliet@example.com/balcony'
type='chat'
xml:lang='en'>
<subject>I implore you!</subject>
<subject
xml:lang='cz'>Úpěnlivě prosim!</subject>
<body>Wherefore art thou, Romeo?</body>
<body xml:lang='cz'>PročeŽ jsi ty, Romeo?</body>
</message>
4.5 Specifying a Conversation Thread
A message stanza MAY contain a child <thread/> element specifying the
conversation thread in which the message is situated, for the purpose
of tracking the conversation (see Thread (Section 2.1.2.3)).
Example: A threaded conversation:
<message
to='romeo@example.net/orchard'
from='juliet@example.com/balcony'
type='chat'>
<body>Art thou not Romeo, and a Montague?</body>
<thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
</message>
<message
to='juliet@example.com/balcony'
from='romeo@example.net/orchard'
type='chat'>
<body>Neither, fair saint, if either thee dislike.</body>
<thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
</message>
<message
to='romeo@example.net/orchard'
from='juliet@example.com/balcony'
type='chat'>
<body>How cam'st thou hither, tell me, and wherefore?</body>
<thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
</message>
Saint-Andre & Miller Expires April 25, 2004 [Page 18]
Internet-Draft XMPP Instant Messaging October 2003
5. Exchanging Presence Information
Exchanging presence information is made relatively straightforward
within XMPP by using presence stanzas. However, we see here a
contrast to the handling of messages: although a client MAY send
directed presence information to another entity, normally presence
information is sent from a client to its server (with no 'to'
address) and then broadcasted by the server to any entities that are
subscribed to the presence of the sending entity. (Note: in the
terminology of RFC 2778 [8], we can say that the only watchers in
XMPP are subscribers.)
For information regarding the syntax of presence stanzas as well as
their defined attributes and child elements, refer to XMPP Core [1].
5.1 Client and Server Presence Responsibilities
After establishing a session, a client SHOULD (but is NOT REQUIRED
to) send initial presence to the server in order to signal its
availability for communications. As defined herein, the initial
presence stanza (1) MUST possess no 'to' address (signalling that it
is meant to be handled by the server on behalf of the client) and (2)
MUST possess no 'type' attribute (signalling the user's
availability).
Upon receiving initial presence from a client, the user's server MUST
do the following:
1. Send presence probes (i.e., presence stanzas whose 'type'
attribute is set to a value of "probe") from the full JID
(<user@somedomain/resource>) of the user to the bare JID
(<contact@otherdomain>) of any contacts to which the user is
subscribed in order to determine if they are available; such
contacts are those which are present in the user's roster with
the 'subscription' attribute set to a value of "to" or "both".
2. Broadcast initial presence from the full JID (<user@somedomain/
resource>) of the user to the bare JID (<contact@otherdomain>) of
any contacts that are subscribed to the user's presence; such
contacts are those which are present in the user's roster with
the 'subscription' attribute set to a value of "from" or "both".
Upon receiving a presence probe from the user, the contact's server
MUST send to the user the last known availability information (i.e.,
the full XML of the last presence stanza) provided by each of the
contact's active sessions (if there exist no active sessions, the
server SHOULD NOT reply to the presence probe). The contact's server
MUST send this information subject to domain-specific access rules,
Saint-Andre & Miller Expires April 25, 2004 [Page 19]
Internet-Draft XMPP Instant Messaging October 2003
and only if the user is in the contact's roster with a subscription
state of "from" or "both" and the contact has not blocked outbound
presence notifications to the user's bare or full JID (as defined
under Blocking Outbound Presence Notifications (Section 10.11)).
(Note: if a server receives a presence probe from a subdomain of the
server's hostname or another such trusted service, it MAY provide
presence information about the user to that entity.)
Upon receiving initial presence from the user, the contact's server
MUST deliver the user's presence stanza to the full JIDs
(<contact@otherdomain/resource>) associated with all of the contact's
active sessions, but only if the user is in the contact's roster with
a subscription state of "to" or "both" and the contact has not
blocked inbound presence notifications from the user's bare or full
JID (as defined under Blocking Inbound Presence Notifications
(Section 10.10)).
If the user's server receives a presence stanza of type "error" in
response to the initial presence that it sent to a contact on behalf
of the user, it SHOULD NOT send further presence updates to that
contact (until and unless it receives a presence probe from the
contact).
After sending initial presence, the user MAY update its presence
information for broadcasting at any time during its active session by
sending a presence stanza with no 'to' address and either no 'type'
attribute or a 'type' attribute with a value of "unavailable". (Note:
a user's client SHOULD NOT send a presence update to broadcast
information that changes independently of the user's presence and
availability.) If the presence stanza lacks a 'type' attribute (i.e.,
expresses availability), the user's server MUST broadcast the full
XML of that presence stanza to all contacts (1) that are in the
user's roster with a subscription type of "from" or "both", (2) to
whom the user has not blocked outbound presence, and (3) from whom
the server has not received a presence error during the user's
session. If the presence stanza has a 'type' attribute set to a value
of "unavailable", the user's server MUST broadcast the full XML of
that presence stanza to all contacts meeting the three conditions
just mentioned, as well as to any entities to which the user has sent
directed available presence during the user's session (if the user
has not yet sent directed unavailable presence to that entity).
A user MAY send directed presence to another entity (i.e., a presence
stanza with a 'to' attribute whose value is the JID of the other
entity and with either no 'type' attribute or a 'type' attribute
whose value is "unavailable"). There are three possible cases:
1. If the user sends directed presence to a contact that is in the
Saint-Andre & Miller Expires April 25, 2004 [Page 20]
Internet-Draft XMPP Instant Messaging October 2003
user's roster with a subscription type of "from" or "both" after
having sent initial presence and before sending unavailable
presence broadcast, the user's server MUST route or deliver the
full XML of that presence stanza (subject to privacy rules) but
SHOULD NOT otherwise modify the contact's status regarding
presence broadcast (i.e., it SHOULD include the contact's JID in
any subsequent presence broadcasts initiated by the user).
2. If the user sends directed presence to an entity that is not in
the user's roster with a subscription type of "from" or "both"
after having sent initial presence and before sending unavailable
presence broadcast, 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 connected resource from which the user
sent the directed presence become unavailable, the user's server
MUST broadcast 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, 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.
Before ending its session with a server, a client SHOULD gracefully
become unavailable by sending a final presence stanza that possesses
no 'to' attribute and that possesses a 'type' attribute whose value
is "unavailable" (optionally, the final presence stanza MAY contain
one or more <status/> elements specifying the reason why the user is
no longer available). However, the user's server MUST NOT depend on
receiving final presence from an available resource, since the
resource may become unavailable unexpectedly. If the user's server
detects that one of the user's resources has become unavailable for
any reason (either gracefully or ungracefully), it MUST broadcast
unavailable presence to all contacts (1) that are in the user's
roster with a subscription type of "from" or "both", (2) to whom the
user has not blocked outbound presence, and (3) from whom the server
has not received a presence error during the user's session; the
user's server MUST also send that unavailable presence stanza to any
entities to which the user has sent directed presence during the
user's session for that resource (if the user has not yet sent
directed unavailable presence to that entity). Any presence stanza
with no 'type' attribute and no 'to' attribute that is sent after
sending directed unavailable presence or broadcasted unavailable
Saint-Andre & Miller Expires April 25, 2004 [Page 21]
Internet-Draft XMPP Instant Messaging October 2003
presence MUST be broadcasted by the server to all subscribers.
5.2 Specifying Availability Status
A client MAY provide further information about its availability
status by using the <show/> element (see Show (Section 2.2.2.1)).
Example: Availability status:
<presence>
<show>dnd</show>
</presence>
5.3 Specifying Detailed Status Information
In conjunction with the <show/> element, a client MAY provide
detailed status information by using the <status/> element (see
Status (Section 2.2.2.2)).
Example: Detailed status information:
<presence xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
<status xml:lang='cz'>Ja dvořím Juliet</status>
</presence>
5.4 Specifying Presence Priority
A client MAY provide a priority for its resource by using the
<priority/> element (see Priority (Section 2.2.2.3)).
Example: Presence priority:
<presence xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
<status xml:lang='cz'>Ja dvořím Juliet</status>
<priority>1</priority>
</presence>
5.5 Presence Examples
The examples in this section illustrate the presence-related
protocols described above. The user is romeo@example.net, he has
Saint-Andre & Miller Expires April 25, 2004 [Page 22]
Internet-Draft XMPP Instant Messaging October 2003
authorized a resource "orchard", and he has the following individuals
in his roster:
o juliet@example.com (subscription="both" and she has two active
sessions, one whose resource is "chamber" and another whose
resource is "balcony")
o benvolio@example.org (subscription="to")
o mercutio@example.org (subscription="from")
Example 1: User sends initial presence:
<presence/>
Example 2: User's server sends presence probes to contacts with
subscription="to" and subscription="both" on behalf of the user's
connected resource:
<presence
type='probe'
from='romeo@example.net/orchard'
to='juliet@example.com'/>
<presence
type='probe'
from='romeo@example.net/orchard'
to='benvolio@example.org'/>
Example 3: User's server sends initial presence to contacts with
subscription="from" and subscription="both" on behalf of the user's
connected resource:
<presence
from='romeo@example.net/orchard'
to='juliet@example.com'/>
<presence
from='romeo@example.net/orchard'
to='mercutio@example.org'/>
Example 4: Contacts' server replies to presence probe on behalf of
all of the contact's available resources:
<presence
from='juliet@example.com/balcony'
to='romeo@example.net/orchard'
xml:lang='en'>
Saint-Andre & Miller Expires April 25, 2004 [Page 23]
Internet-Draft XMPP Instant Messaging October 2003
<show>away</show>
<status>be right back</status>
<priority>0</priority>
</presence>
<presence
from='juliet@example.com/chamber'
to='romeo@example.net/orchard'>
<priority>1</priority>
</presence>
<presence
from='benvolio@example.org/pda'
to='romeo@example.net/orchard'
xml:lang='en'>
<show>dnd</show>
<status>gallivanting</status>
</presence>
Example 5: Contact's server delivers user's initial presence to all
of the contact's available resources or returns error to user:
<presence
from='romeo@example.net/orchard'
to='juliet@example.com/chamber'/>
<presence
from='romeo@example.net/orchard'
to='juliet@example.com/balcony'/>
<presence
type='error'
from='mercutio@example.org'
to='romeo@example.net/orchard'>
<error type='cancel'>
<gone xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</presence>
Example 6: User sends directed presence to another user not in his
roster:
<presence
from='romeo@example.net/orchard'
to='nurse@example.com'
xml:lang='en'>
<show>dnd</show>
<status>courting Juliet</status>
Saint-Andre & Miller Expires April 25, 2004 [Page 24]
Internet-Draft XMPP Instant Messaging October 2003
<priority>0</priority>
</presence>
Example 7: User sends updated available presence information for
broadcasting:
<presence xml:lang='en'>
<show>away</show>
<status>I shall return!</status>
<priority>1</priority>
</presence>
Example 8: Updated presence information is delivered only to one
contact (not those from whom an error was received or to whom the
user sent directed presence):
<presence
from='romeo@example.net/orchard'
to='juliet@example.com/chamber'
xml:lang='en'>
<show>away</show>
<status>I shall return!</status>
<priority>1</priority>
</presence>
<presence
from='romeo@example.net/orchard'
to='juliet@example.com/balcony'
xml:lang='en'>
<show>away</show>
<status>I shall return!</status>
<priority>1</priority>
</presence>
Example 9: One of the contact's resources sends final presence:
<presence type='unavailable'/>
Example 10: Contact's server sends unavailable presence information
to user:
<presence
type='unavailable'
from='juliet@example.com/balcony'
to='romeo@example.net/orchard'/>
Example 11: User sends final presence:
Saint-Andre & Miller Expires April 25, 2004 [Page 25]
Internet-Draft XMPP Instant Messaging October 2003
<presence type='unavailable' xml:lang='en'>
<status>gone home</status>
</presence>
Example 12: Unavailable presence information is delivered to
contact's one remaining resource as well as to the person to whom the
user sent directed presence:
<presence
type='unavailable'
from='romeo@example.net/orchard'
to='juliet@example.com/chamber'
xml:lang='en'>
<status>gone home</status>
</presence>
<presence
from='romeo@example.net/orchard'
to='nurse@example.com'
xml:lang='en'>
<status>gone home</status>
</presence>
6. Managing Subscriptions
In order to protect the privacy of instant messaging users and any
other entities, presence and availability 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 information. A
subscription lasts across sessions; indeed, it lasts until the
subscriber unsubscribes or the subscribee cancels the
previously-granted subscription. Subscriptions are managed within
XMPP by sending presence stanzas containing specially-defined
attributes.
Note: there are important interactions between subscriptions and
rosters; these are defined under Integration of Roster Items and
Presence Subscriptions (Section 8), and the reader must refer to that
section for a complete understanding of presence subscriptions.
6.1 Requesting a Subscription
A request to subscribe to another entity's presence is made by
sending a presence stanza of type "subscribe".
Example: Sending a subscription request:
Saint-Andre & Miller Expires April 25, 2004 [Page 26]
Internet-Draft XMPP Instant Messaging October 2003
<presence to='juliet@example.com' type='subscribe'/>
If the subscription request is being sent to another instant
messaging user, the JID supplied in the 'to' attribute SHOULD be of
the form <contact@otherdomain> rather than <contact@otherdomain/
resource>.
A user's server MUST NOT automatically approve subscription requests
on the user's behalf. All subscription requests MUST be directed to
the user's client. If there is no available resource associated with
the user when the subscription request is received by the server, the
user's server MUST store the subscription request offline for
delivery when the user next becomes available. (Note: if a resource
has authorized a session but has not provided initial presence, the
server SHOULD NOT consider it to be available and therefore SHOULD
NOT send subscription requests to it.)
6.2 Handling a Subscription Request
When a client receives a subscription request from another entity, it
MUST either approve the request by sending a presence stanza of type
"subscribed" or refuse the request by sending a presence stanza of
type "unsubscribed".
Example: Approving a subscription request:
<presence to='romeo@example.net' type='subscribed'/>
Example: Refusing a presence subscription request:
<presence to='romeo@example.net' type='unsubscribed'/>
6.3 Cancelling a Subscription from Another Entity
If a user would like to cancel a previously-granted subscription
request, it sends a presence stanza of type "unsubscribed".
Example: Cancelling a previously granted subscription request:
<presence to='romeo@example.net' type='unsubscribed'/>
6.4 Unsubscribing from Another Entity's Presence
If a user would like to unsubscribe from the presence of another
entity, it sends a presence stanza of type "unsubscribe".
Saint-Andre & Miller Expires April 25, 2004 [Page 27]
Internet-Draft XMPP Instant Messaging October 2003
Example: Unsubscribing from an entity's presence:
<presence to='juliet@example.com' type='unsubscribe'/>
7. Roster Management
In XMPP, one's contact list is called a roster, which consists of any
number of specific roster items, each roster item being identified by
a unique JID (usually of the form <contact@otherdomain>). 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 available resource.
Note: there are important interactions between rosters and
subscriptions; these are defined under Integration of Roster Items
and Presence Subscriptions (Section 8), and the reader must refer to
that section for a complete understanding of roster management.
7.1 Syntax and Semantics
Rosters are managed using IQ stanzas, specifically by means of a
<query/> child element qualified by the 'jabber:iq:roster' namespace.
The <query/> element MAY contain one or more <item/> children, each
describing a unique roster item or "contact".
The "key" or unique identifier for each roster item is a JID,
encapsulated in the required 'jid' attribute of the <item/> element.
The value of the 'jid' attribute SHOULD be of the form
<user@somedomain>, especially if the item is associated with another
(human) instant messaging user.
The state of the presence subscription in relation to a roster item
is captured in the 'subscription' attribute of the <item/> element.
Allowable values for this attribute are:
o "none" -- the user does not have a subscription to the contact,
and the contact does not have a subscription to the user
o "to" -- the user has a subscription to the contact, but the
contact does not have a subscription to the user
o "from" -- the contact has a subscription to the user, but the user
does not have a subscription to the contact
o "both" -- both the user and the contact have subscriptions to each
other
Each <item/> element MAY contain a 'name' attribute, which sets the
Saint-Andre & Miller Expires April 25, 2004 [Page 28]
Internet-Draft XMPP Instant Messaging October 2003
"nickname" to be associated with the JID, as determined by the user
(not the contact). The value of the 'name' attribute is opaque.
Each <item/> element MAY contain one or more <group/> child elements,
for use in collecting roster items into various categories. The CDATA
text of the <group/> element is opaque.
7.2 Business Rules
A server MUST ignore any 'to' address on a roster "set", and MUST
treat any roster "set" as applying to the sender. For added safety, a
client SHOULD check the "from" address of a roster "push" to ensure
that it is from a trusted source; specifically, the stanza SHOULD
have no 'from' attribute (i.e., implicitly from the server) or the
JID contained in the 'from' attribute SHOULD match the user's bare
JID or full JID; otherwise, the client SHOULD ignore the roster
"push".
7.3 Retrieving One's Roster on Login
Upon connecting to the server, a client SHOULD request the roster
(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 NOT REQUIRED). If an available resource
does not request the roster during a session, the server SHOULD NOT
send it presence subscriptions and associated roster updates.
Example: Client requests current roster from server:
<iq from='juliet@example.com/balcony' type='get' id='roster_1'>
<query xmlns='jabber:iq:roster'/>
</iq>
Example: Client receives roster from the server:
<iq to='juliet@example.com/balcony' type='result' id='roster_1'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
name='Romeo'
subscription='both'>
<group>Friends</group>
</item>
<item jid='mercutio@example.org'
name='Mercutio'
subscription='from'>
<group>Friends</group>
</item>
<item jid='benvolio@example.org'
Saint-Andre & Miller Expires April 25, 2004 [Page 29]
Internet-Draft XMPP Instant Messaging October 2003
name='Benvolio'
subscription='both'>
<group>Friends</group>
</item>
</query>
</iq>
7.4 Adding a Roster Item
At any time, a user MAY add an item to his or her roster.
Example: Client adds a new item:
<iq from='juliet@example.com/balcony' type='set' id='roster_2'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'>
<group>Servants</group>
</item>
</query>
</iq>
The server MUST update the roster information in persistent storage,
and also push the change out to all of the user's available resources
that have requested the roster. This "roster push" consists of an IQ
set from the server to the client and enables all available resources
to remain in sync with the server-based roster information.
Example: Server (1) pushes the updated roster information to all
available resources and (2) replies with an IQ result to the sending
resource:
<iq to='juliet@example.com/balcony' type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'
subscription='none'>
<group>Servants</group>
</item>
</query>
</iq>
<iq to='juliet@example.com/chamber' type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'
subscription='none'>
Saint-Andre & Miller Expires April 25, 2004 [Page 30]
Internet-Draft XMPP Instant Messaging October 2003
<group>Servants</group>
</item>
</query>
</iq>
<iq to='juliet@example.com/balcony' type='result' id='roster_2'/>
Example: Connected resources reply with an IQ result to the server:
<iq from='juliet@example.com/balcony'
to='example.com'
type='result'/>
<iq from='juliet@example.com/chamber'
to='example.com'
type='result'/>
7.5 Updating a Roster Item
Updating an existing roster item (e.g., changing the group) is done
in the same way as adding a new roster item, i.e., by sending the
roster item in an IQ set to the server.
Example: User updates roster item (added group):
<iq from='juliet@example.com/chamber' type='set' id='roster_3'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
name='Romeo'
subscription='both'>
<group>Friends</group>
<group>Lovers</group>
</item>
</query>
</iq>
As with adding a roster item, when updating a roster item the server
MUST update the roster information in persistent storage, and also
initiate a roster push to all of the user's available resources that
have requested the roster.
7.6 Deleting a Roster Item
At any time, a user MAY delete an item from its roster by doing an IQ
set and making sure that the value of the 'subscription' attribute is
"remove" (a compliant server MUST ignore any other values of the
'subscription' attribute when received from a client).
Saint-Andre & Miller Expires April 25, 2004 [Page 31]
Internet-Draft XMPP Instant Messaging October 2003
Example: Client removes an item:
<iq from='juliet@example.com/balcony' type='set' id='roster_4'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com' subscription='remove'/>
</query>
</iq>
As with adding a roster item, when deleting a roster item the server
MUST update the roster information in persistent storage, initiate a
roster push to all of the user's available resources that have
requested the roster (with the 'subscription' attribute set to a
value of "remove"), and send an IQ result to the initiating resource.
For further information about the implications of this command, see
Removing a Roster Item and Cancelling All Subscriptions (Section
8.6).
8. Integration of Roster Items and Presence Subscriptions
8.1 Overview
Some level of integration between roster items and presence
subscriptions is normally expected by an instant messaging user
regarding the user's subscriptions to and from other contacts. This
section describes the level of integration that MUST be supported
within XMPP instant messaging applications.
There are four primary subscription states:
o None -- Neither the user nor the contact is subscribed to the
other's presence
o To -- The user is subscribed to the contact's presence but there
is no subscription from the contact to the user
o From -- There is a subscription from the contact to the user, but
the user has not subscribed to the contact's presence
o Both -- Both the user and the contact are subscribed to each
other's presence (i.e., the union of 'from' and 'to')
Each of these states is reflected in the roster of both the user and
the contact, thus resulting in durable subscription states. Narrative
explanations of how these subscription states interact with roster
items in order to complete certain defined use cases are provided in
the following sub-sections. Full details regarding server and client
handling of all subscription states (including pending states between
Saint-Andre & Miller Expires April 25, 2004 [Page 32]
Internet-Draft XMPP Instant Messaging October 2003
the primary states listed above) is provided in Subscription States
(Section 9).
If a connected resource does not both send initial presence and
request the roster, the server SHOULD NOT send it presence
subscription requests or roster pushes.
The 'from' and 'to' addresses are OPTIONAL in roster pushes; if
included, their values SHOULD be the full JID of the resource for
that session. A client MUST acknowledge each roster push with an IQ
stanza of type "result" (for the sake of brevity, these stanzas are
not shown in the following examples but are required by XMPP Core
[1]).
8.2 User Subscribes to Contact
The process by which a user subscribes to a contact, including the
interaction between roster items and subscription states, is defined
below.
1. In preparation for being able to render the contact in the user's
client interface and for the server to keep track of the
subscription, the user's client SHOULD perform a "roster set" for
the new roster item. This request consists of an IQ stanza of
type='set' containing a <query/> element in the
'jabber:iq:roster' namespace, which in turn contains an <item/>
element that defines the new roster item; the <item/> element
MUST possess a 'jid' attribute, MAY possess a 'name' attribute,
MUST NOT possess a 'subscription' attribute, and MAY contain one
or more <group/> child elements:
<iq type='set' id='int1'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@otherdomain'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
2. As a result, the user's server (1) MUST initiate a roster push
for the new roster item to all available resources associated
with this user that have requested the roster, setting the
'subscription' attribute to a value of "none"; and (2) MUST reply
with an IQ stanza of type='result':
<iq type='set'>
Saint-Andre & Miller Expires April 25, 2004 [Page 33]
Internet-Draft XMPP Instant Messaging October 2003
<query xmlns='jabber:iq:roster'>
<item
jid='contact@otherdomain'
subscription='none'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
<iq type='result' id='int1'/>
3. If the user wants to request a subscription to the contact's
presence, the user's client MUST send a presence stanza of
type='subscribe' to the contact:
<presence to='contact@otherdomain' type='subscribe'/>
4. As a result, the user's server MUST initiate a second roster push
to all of the user's available resources that have requested the
roster, setting the contact to the pending sub-state of the
'none' subscription state; this pending sub-state is denoted by
the inclusion of the ask='subscribe' attribute in the roster
item:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@otherdomain'
subscription='none'
ask='subscribe'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
Note: if the user did not create a roster item before sending the
subscription request, the server MUST now create one on behalf of
the user and send a roster push to all of the user's available
resources that have requested the roster, absent the 'name'
attribute and the <group/> child.
5. The user's server MUST also stamp the presence stanza of type
"subscribe" with the user's bare JID (i.e., <user@somedomain>) as
the 'from' address. If the contact is served by a different host
than the user, the user's server MUST route the presence stanza
to the contact's server for delivery to the contact (this case is
Saint-Andre & Miller Expires April 25, 2004 [Page 34]
Internet-Draft XMPP Instant Messaging October 2003
assumed throughout; however, if the contact is served by the same
host, then the server can simply deliver the presence stanza
directly):
<presence
from='user@somedomain'
to='contact@otherdomain'
type='subscribe'/>
6. Upon receiving the presence stanza of type "subscribe" addressed
to the contact, the contact's server must determine if there is
at least one active session in which the contact has sent
available presence and has requested the roster. If so, it MUST
deliver the subscription request to the contact (if not, the
contact's server MUST store the subscription request offline for
delivery when this condition is next met). No matter when the
subscription request is delivered, the contact must decide
whether or not to approve it (subject to configured preferences,
the contact's client MAY approve or refuse the subscription
request without presenting it to the contact). Here we assume the
"happy path" that the contact approves the subscription request
(the alternate flow of declining the subscription request is
defined in Section 8.2.1). In this case, the contact's client (1)
SHOULD perform a roster set specifying the desired nickname and
group for the user (if any); and (2) MUST send a presence stanza
of type "subscribed" to the user in order to approve the
subscription request.
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@somedomain'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence to='user@somedomain' type='subscribed'/>
7. As a result, the contact's server (1) MUST initiate a roster push
to all available resources associated with the contact that have
requested the roster, containing a roster item for the user with
the subscription state set to 'from'; (2) MUST route the presence
stanza of type "subscribed" to the user; and (3) MUST send
available presence from all of the contact's available resources
to the user:
Saint-Andre & Miller Expires April 25, 2004 [Page 35]
Internet-Draft XMPP Instant Messaging October 2003
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@somedomain'
subscription='from'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='contact@otherdomain/resource'
to='user@somedomain'
type='subscribed'/>
<presence
from='contact@otherdomain/resource'
to='user@somedomain'/>
8. Upon receiving the presence stanza of type "subscribed" addressed
to the user, the user's server MUST first verify that the contact
is in the user's roster with either of the following states: (a)
subscription='none' and ask='subscribe' or (b)
subscription='from' and ask='subscribe'. If the contact is not in
the user's roster with either of those states, the user's server
MUST silently ignore the presence stanza of type "subscribed"
(i.e., it MUST NOT route it to the user, modify the user's
roster, or generate a roster push to the user's available
resources). If the contact is in the user's roster with either of
those states, the user's server (1) MUST deliver the presence
stanza of type "subscribed" from the contact to the user; (2)
MUST initiate a roster push to all of the user's available
resources that have requested the roster, containing an updated
roster item for the contact with the 'subscription' attribute set
to a value of "to"; and (3) MUST deliver the available presence
stanza received from each of the contact's available resources to
each of the user's available resources:
<presence
to='user@somedomain'
from='contact@otherdomain'
type='subscribed'/>
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@otherdomain'
Saint-Andre & Miller Expires April 25, 2004 [Page 36]
Internet-Draft XMPP Instant Messaging October 2003
subscription='to'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
<presence
from='contact@otherdomain/resource'
to='user@somedomain/resource'/>
9. Upon receiving the presence stanza of type "subscribed", the user
SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "subscribe" to the contact or "denying" it by
sending a presence stanza of type "unsubscribe" to the contact;
this step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the user's server know that it MUST no longer send notification
of the subscription state change to the user (see Section 9.6).
From the perspective of the user, there now exists a subscription to
the contact; from the perspective of the contact, there now exists a
subscription from the user. (Note: If at this point the user sends
another subscription request to the contact, the user's server MUST
silently ignore that request.)
8.2.1 Alternate Flow: Contact Declines Subscription Request
The above activity flow represents the "happy path" related to the
user's subscription request to the contact. The main alternate flow
occurs if the contact refuses the user's subscription request.
1. If the contact wants to refuse the request, the contact's client
MUST send a presence stanza of type "unsubscribed" to the user
(instead of the presence stanza of type "subscribed" sent in Step
6 of Section 8.2):
<presence to='user@somedomain' type='unsubscribed'/>
2. As a result, the contact's server MUST route the presence stanza
of type "unsubscribed" to the user, first stamping the 'from'
address as the bare JID (<contact@otherdomain>) of the contact:
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unsubscribed'/>
Saint-Andre & Miller Expires April 25, 2004 [Page 37]
Internet-Draft XMPP Instant Messaging October 2003
3. Upon receiving the presence stanza of type "unsubscribed"
addressed to the user, the user's server (1) MUST deliver that
presence stanza to the user and (2) MUST initiate a roster push
to all of the user's available resources that have requested the
roster, containing an updated roster item for the contact with
the 'subscription' attribute set to a value of "none" and with no
'ask' attribute:
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unsubscribed'/>
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@otherdomain'
subscription='none'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
4. Upon receiving the presence stanza of type "unsubscribed", the
user SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribe" to the contact or "denying" it by
sending a presence stanza of type "subscribe" to the contact;
this step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the user's server know that it MUST no longer send notification
of the subscription state change to the user (see Section 9.6).
As a result of this activity, the contact is now in the user's roster
with a subscription state of "none", whereas the user is not in the
contact's roster at all.
8.3 Creating a Mutual Subscription
The user and contact can build on the foregoing to create a mutual
subscription (i.e., a subscription of type "both"). The process is
defined below.
1. If the contact wants to create a mutual subscription, the contact
MUST send a subscription request to the user (subject to
configured preferences, the contact's client MAY send this
automatically):
Saint-Andre & Miller Expires April 25, 2004 [Page 38]
Internet-Draft XMPP Instant Messaging October 2003
<presence to='user@somedomain' type='subscribe'/>
2. As a result, the contact's server (1) MUST initiate a roster push
to all available resources associated with the contact that have
requested the roster, with the user still in the 'from'
subscription state but with a pending 'to' subscription denoted
by the inclusion of the ask='subscribe' attribute in the roster
item; and (2) MUST route the presence stanza of type "subscribe"
to the user, first stamping the 'from' address as the bare JID
(<contact@otherdomain>) of the contact:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@somedomain'
subscription='from'
ask='subscribe'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='contact@otherdomain'
to='user@somedomain'
type='subscribe'/>
3. Upon receiving the presence stanza of type "subscribe" addressed
to the user, the user's server must determine if there is at
least one active session in which the user has sent available
presence and has requested the roster. If so, the user's server
MUST deliver the subscription request to the user (if not, it
MUST store the subscription request offline for delivery when
this condition is next met). No matter when the subscription
request is delivered, the user must then decide whether or not to
approve it (subject to configured preferences, the user's client
MAY approve or refuse the subscription request without presenting
it to the user). Here we assume the "happy path" that the user
approves the subscription request (the alternate flow of
declining the subscription request is defined in Section 8.3.1).
In this case, the user's client MUST send a presence stanza of
type "subscribed" to the contact in order to approve the
subscription request.
<presence to='contact@otherdomain' type='subscribed'/>
Saint-Andre & Miller Expires April 25, 2004 [Page 39]
Internet-Draft XMPP Instant Messaging October 2003
4. As a result, the user's server (1) MUST initiate a roster push to
all of the user's available resources that have requested the
roster, containing a roster item for the contact with the
'subscription' attribute set to a value of "both"; (2) MUST route
the presence stanza of type "subscribed" to the contact, first
stamping the 'from' address as the bare JID (<user@somedomain>)
of the user; and (3) MUST send available presence from each of
the user's available resources to the contact:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@otherdomain'
subscription='both'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
<presence
from='user@somedomain'
to='contact@otherdomain'
type='subscribed'/>
<presence
from='user@somedomain/resource'
to='contact@otherdomain'/>
5. Upon receiving the presence stanza of type "subscribed" addressed
to the contact, the contact's server MUST first verify that the
user is in the contact's roster with either of the following
states: (a) subscription='none' and ask='subscribe' or (b)
subscription='from' and ask='subscribe'. If the user is not in
the contact's roster with either of those states, the contact's
server MUST silently ignore the presence stanza of type
"subscribed" (i.e., it MUST NOT route it to the contact, modify
the contact's roster, or generate a roster push to the contact's
available resources). If the user is in the contact's roster with
either of those states, the contact's server (1) MUST deliver the
presence stanza of type "subscribed" from the user to the
contact; (2) MUST initiate a roster push to all available
resources associated with the contact that have requested the
roster, containing an updated roster item for the user with the
'subscription' attribute set to a value of "both"; and (3) MUST
deliver the available presence stanza received from each of the
user's available resources to each of the contact's available
resources:
Saint-Andre & Miller Expires April 25, 2004 [Page 40]
Internet-Draft XMPP Instant Messaging October 2003
<presence
from='user@somedomain'
to='contact@otherdomain'
type='subscribed'/>
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@somedomain'
subscription='both'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='user@somedomain/resource'
to='contact@otherdomain/resource'/>
6. Upon receiving the presence stanza of type "subscribed", the
contact SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "subscribe" to the user or "denying" it by sending
a presence stanza of type "unsubscribe" to the user; this step
does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the contact's server know that it MUST no longer send
notification of the subscription state change to the contact (see
Section 9.6).
The user and the contact now have a mutual subscription to each
other's presence -- i.e., the subscription is of type "both". The
user's server MUST now send the user's current presence information
to the contact. (Note: If at this point the user sends a subscription
request to the contact or the contact sends a subscription request to
the user, the sending user's server MUST silently ignore that request
and not route it to the intended recipient.)
8.3.1 Alternate Flow: User Declines Subscription Request
The above activity flow represents the "happy path" related to the
contact's subscription request to the user. The main alternate flow
occurs if the user refuses the contact's subscription request.
1. If the user wants to refuse the request, the user's client MUST
send a presence stanza of type "unsubscribed" to the contact
(instead of the presence stanza of type "subscribed" sent in Step
Saint-Andre & Miller Expires April 25, 2004 [Page 41]
Internet-Draft XMPP Instant Messaging October 2003
3 of Section 8.3):
<presence to='contact@otherdomain' type='unsubscribed'/>
2. As a result, the user's server MUST route the presence stanza of
type "unsubscribed" to the contact, first stamping the 'from'
address as the bare JID (<user@somedomain>) of the user:
<presence
from='user@somedomain'
to='contact@otherdomain'
type='unsubscribed'/>
3. Upon receiving the presence stanza of type "unsubscribed"
addressed to the contact, the contact's server (1) MUST deliver
that presence stanza to the contact; and (2) MUST initiate a
roster push to all available resources associated with the
contact that have requested the roster, containing an updated
roster item for the user with the 'subscription' attribute set to
a value of "from" and with no 'ask' attribute:
<presence
from='user@somedomain'
to='contact@otherdomain'
type='unsubscribed'/>
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@somedomain'
subscription='from'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
4. Upon receiving the presence stanza of type "unsubscribed", the
contact SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribe" to the user or "denying" it by
sending a presence stanza of type "subscribe" to the user; this
step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the contact's server know that it MUST no longer send
notification of the subscription state change to the contact (see
Section 9.6).
Saint-Andre & Miller Expires April 25, 2004 [Page 42]
Internet-Draft XMPP Instant Messaging October 2003
As a result of this activity, there has been no change in the
subscription state; i.e., the contact is in the user's roster with a
subscription state of "to" and the user is in the contact's roster
with a subscription state of "from".
8.4 Unsubscribing
At any time after subscribing to a contact's presence, a user MAY
unsubscribe. While the XML that the user sends to make this happen is
the same in all instances, the subsequent subscription state is
different depending on the subscription state obtaining when the
unsubscribe "command" is sent. Both possible scenarios are defined
below.
8.4.1 Case #1: Unsubscribing When Subscription is Not Mutual
In the first case, the user has a subscription to the contact but the
contact does not have a subscription to the user (i.e., the
subscription is not yet mutual).
1. If the user wants to unsubscribe from the contact's presence, the
user MUST send a presence stanza of type "unsubscribe" to the
contact:
<presence to='contact@otherdomain' type='unsubscribe'/>
2. As a result, the user's server (1) MUST send a roster push to all
of the user's available resources that have requested the roster,
containing an updated roster item for the contact with the
'subscription' attribute set to a value of "none"; and (2) MUST
route the presence stanza of type "unsubscribe" to the contact,
first stamping the 'from' address as the bare JID
(<user@somedomain>) of the user:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@otherdomain'
subscription='none'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
<presence
from='user@somedomain'
to='contact@otherdomain'
Saint-Andre & Miller Expires April 25, 2004 [Page 43]
Internet-Draft XMPP Instant Messaging October 2003
type='unsubscribe'/>
3. Upon receiving the presence stanza of type "unsubscribe"
addressed to the contact, the contact's server (1) MUST initiate
a roster push to all available resources associated with the
contact that have requested the roster, containing an updated
roster item for the user with the 'subscription' attribute set to
a value of "none" (if the contact is offline, the contact's
server MUST modify the roster item and send that modified item
the next time the contact requests the roster); and (2) MUST
deliver the "unsubscribe" state change notification to the
contact:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@somedomain'
subscription='none'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='user@somedomain'
to='contact@otherdomain'
type='unsubscribe'/>
4. Upon receiving the presence stanza of type "unsubscribe", the
contact SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribed" to the user or "denying" it by
sending a presence stanza of type "subscribed" to the user; this
step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the contact's server know that it MUST no longer send
notification of the subscription state change to the contact (see
Section 9.6).
5. The contact's server then (1) MUST send a presence stanza of type
"unsubscribed" to the user; and (2) SHOULD send unavailable
presence from the contact to the user:
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unsubscribed'/>
Saint-Andre & Miller Expires April 25, 2004 [Page 44]
Internet-Draft XMPP Instant Messaging October 2003
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unavailable'/>
6. When the user's server receives a presence stanza of type
"unsubscribed" and/or unavailable presence, it MUST deliver them
to the user:
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unsubscribed'/>
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unavailable'/>
7. Upon receiving the presence stanza of type "unsubscribed", the
user SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribe" to the contact or "denying" it by
sending a presence stanza of type "subscribe" to the contact;
this step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the user's server know that it MUST no longer send notification
of the subscription state change to the user (see Section 9.6).
8.4.2 Case #2: Unsubscribing When Subscription is Mutual
In the second case, the user has a subscription to the contact and
the contact also has a subscription to the user (i.e., the
subscription is mutual).
1. If the user wants to unsubscribe from the contact's presence, the
user MUST send a presence stanza of type "unsubscribe" to the
contact:
<presence to='contact@otherdomain' type='unsubscribe'/>
2. As a result, the user's server (1) MUST send a roster push to all
of the user's available resources that have requested the roster,
containing an updated roster item for the contact with the
'subscription' attribute set to a value of "from"; and (2) MUST
route the presence stanza of type "unsubscribe" to the contact,
first stamping the 'from' address as the bare JID
Saint-Andre & Miller Expires April 25, 2004 [Page 45]
Internet-Draft XMPP Instant Messaging October 2003
(<user@somedomain>) of the user:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@otherdomain'
subscription='from'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
<presence
from='user@somedomain'
to='contact@otherdomain'
type='unsubscribe'/>
3. Upon receiving the presence stanza of type "unsubscribe"
addressed to the contact, the contact's server (1) MUST initiate
a roster push to all available resources associated with the
contact that have requested the roster, containing an updated
roster item for the user with the 'subscription' attribute set to
a value of "to" (if the contact is offline, the contact's server
MUST modify the roster item and send that modified item the next
time the contact requests the roster); and (2) MUST deliver the
"unsubscribe" state change notification to the contact:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@somedomain'
subscription='to'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='user@somedomain'
to='contact@otherdomain'
type='unsubscribe'/>
4. Upon receiving the presence stanza of type "unsubscribe", the
contact SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribed" to the user or "denying" it by
Saint-Andre & Miller Expires April 25, 2004 [Page 46]
Internet-Draft XMPP Instant Messaging October 2003
sending a presence stanza of type "subscribed" to the user; this
step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the contact's server know that it MUST no longer send
notification of the subscription state change to the contact (see
Section 9.6).
5. The contact's server then (1) MUST send a presence stanza of type
"unsubscribed" to the user; and (2) SHOULD send unavailable
presence from the contact to the user:
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unsubscribed'/>
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unavailable'/>
6. When the user's server receives a presence stanza of type
"unsubscribed" and/or unavailable presence, it MUST deliver them
to the user:
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unsubscribed'/>
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unavailable'/>
7. Upon receiving the presence stanza of type "unsubscribed", the
user SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribe" to the contact or "denying" it by
sending a presence stanza of type "subscribe" to the contact;
this step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the user's server know that it MUST no longer send notification
of the subscription state change to the user (see Section 9.6).
Note: Obviously this does not result in removal of the roster item
from the user's roster, and the contact still has a subscription to
the user's presence. In order to both completely cancel a mutual
Saint-Andre & Miller Expires April 25, 2004 [Page 47]
Internet-Draft XMPP Instant Messaging October 2003
subscription and fully remove the roster item from the user's roster,
the user SHOULD update the roster item with subscription='remove' as
defined under Removing a Roster Item and Cancelling All Subscriptions
(Section 8.6).
8.5 Cancelling a Subscription
At any time after approving a subscription request from a user, a
contact MAY cancel that subscription. While the XML that the contact
sends to make this happen is the same in all instances, the
subsequent subscription state is different depending on the
subscription state obtaining when the cancellation was sent. Both
possible scenarios are defined below.
8.5.1 Case #1: Cancelling When Subscription is Not Mutual
In the first case, the user has a subscription to the contact but the
contact does not have a subscription to the user (i.e., the
subscription is not yet mutual).
1. If the contact wants to cancel the user's subscription, the
contact MUST send a presence stanza of type "unsubscribed" to the
user:
<presence to='user@somedomain' type='unsubscribed'/>
2. As a result, the contact's server (1) MUST send a roster push to
all of the contact's available resources that have requested the
roster, containing an updated roster item for the user with the
'subscription' attribute set to a value of "none"; (2) MUST route
the presence stanza of type "unsubscribed" to the user, first
stamping the 'from' address as the bare JID
(<contact@otherdomain>) of the contact; and (3) SHOULD send
unavailable presence from the contact to the user:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@somedomain'
subscription='none'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='contact@otherdomain'
Saint-Andre & Miller Expires April 25, 2004 [Page 48]
Internet-Draft XMPP Instant Messaging October 2003
to='user@somedomain'
type='unsubscribed'/>
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unavailable'/>
3. Upon receiving the presence stanza of type "unsubscribed"
addressed to the user, the user's server (1) MUST initiate a
roster push to all of the user's available resources that have
requested the roster, containing an updated roster item for the
contact with the 'subscription' attribute set to a value of
"none" (if the user is offline, the user's server MUST modify the
roster item and send that modified item the next time the user
requests the roster); (2) MUST deliver the "unsubscribed" state
change notification to the user; and (3) MUST deliver the
unavailable presence to the user:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@otherdomain'
subscription='none'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unsubscribed'/>
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unavailable'/>
4. Upon receiving the presence stanza of type "unsubscribed", the
user SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribe" to the contact or "denying" it by
sending a presence stanza of type "subscribe" to the contact;
this step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the user's server know that it MUST no longer send notification
Saint-Andre & Miller Expires April 25, 2004 [Page 49]
Internet-Draft XMPP Instant Messaging October 2003
of the subscription state change to the user (see Section 9.6).
8.5.2 Case #2: Cancelling When Subscription is Mutual
In the second case, the user has a subscription to the contact and
the contact also has a subscription to the user (i.e., the
subscription is mutual).
1. If the contact wants to cancel the user's subscription, the
contact MUST send a presence stanza of type "unsubscribed" to the
user:
<presence to='user@somedomain' type='unsubscribed'/>
2. As a result, the contact's server (1) MUST send a roster push to
all of the contact's available resources that have requested the
roster, containing an updated roster item for the user with the
'subscription' attribute set to a value of "to"; (2) MUST route
the presence stanza of type "unsubscribed" to the user, first
stamping the 'from' address as the bare JID
(<contact@otherdomain>) of the contact; and (3) SHOULD send
unavailable presence from the contact to the user:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@somedomain'
subscription='to'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unsubscribed'/>
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unavailable'/>
3. Upon receiving the presence stanza of type "unsubscribed"
addressed to the user, the user's server (1) MUST initiate a
roster push to all of the user's available resources that have
Saint-Andre & Miller Expires April 25, 2004 [Page 50]
Internet-Draft XMPP Instant Messaging October 2003
requested the roster, containing an updated roster item for the
contact with the 'subscription' attribute set to a value of
"from" (if the user is offline, the user's server MUST modify the
roster item and send that modified item the next time the user
requests the roster); and (2) MUST deliver the "unsubscribed"
state change notification to the user; and (3) MUST deliver the
unavailable presence to the user:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@otherdomain'
subscription='from'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unsubscribed'/>
<presence
from='contact@otherdomain'
to='user@somedomain'
type='unavailable'/>
4. Upon receiving the presence stanza of type "unsubscribed", the
user SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribe" to the contact or "denying" it by
sending a presence stanza of type "subscribe" to the contact;
this step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the user's server know that it MUST no longer send notification
of the subscription state change to the user (see Section 9.6).
Note: Obviously this does not result in removal of the roster item
from the contact's roster, and the contact still has a subscription
to the user's presence. In order to both completely cancel a mutual
subscription and fully remove the roster item from the contact's
roster, the contact should update the roster item with
subscription='remove' as defined under Removing a Roster Item and
Cancelling All Subscriptions (Section 8.6).
Saint-Andre & Miller Expires April 25, 2004 [Page 51]
Internet-Draft XMPP Instant Messaging October 2003
8.6 Removing a Roster Item and Cancelling All Subscriptions
Because there may be many steps involved in completely removing a
roster item and cancelling subscriptions in both directions, the
roster management protocol includes a "shortcut" method for doing so.
The process may be initiated no matter what the current subscription
state is by sending a roster set containing an item for the contact
with the 'subscription' attribute set to a value of "remove":
<iq type='set' id='remove1'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@otherdomain'
subscription='remove'/>
</query>
</iq>
When the user removes a contact from his or her roster by setting the
'subscription' attribute to a value of "remove", the user's server
(1) MUST automatically cancel any existing presence subscription
between the user and the contact (both 'to' and 'from' as
appropriate); (2) MUST remove the roster item from the user's roster
and inform all of the user's available resources of the roster item
removal; (3) MUST inform the resource that initiated the removal of
success; and (4) SHOULD send unavailable presence to the contact:
<presence
from='user@somedomain'
to='contact@otherdomain'
type='unsubscribe'/>
<presence
from='user@somedomain'
to='contact@otherdomain'
type='unsubscribed'/>
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@otherdomain'
subscription='remove'/>
</query>
</iq>
<iq type='result' id='remove1'/>
<presence
from='user@somedomain'
Saint-Andre & Miller Expires April 25, 2004 [Page 52]
Internet-Draft XMPP Instant Messaging October 2003
to='contact@otherdomain'
type='unavailable'/>
Upon receiving the presence stanza of type "unsubscribe", the
contact's server (1) MUST initiate a roster push to all available
resources associated with the contact that have requested the roster,
containing an updated roster item for the user with the
'subscription' attribute set to a value of "to" (if the contact is
offline, the contact's server MUST modify the roster item and send
that modified item the next time the contact requests the roster);
and (2) MUST also deliver the "unsubscribe" state change notification
to the contact:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@somedomain'
subscription='to'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='user@somedomain'
to='contact@otherdomain'
type='unsubscribe'/>
Upon receiving the presence stanza of type "unsubscribed", the
contact's server (1) MUST initiate a roster push to all available
resources associated with the contact that have requested the roster,
containing an updated roster item for the user with the
'subscription' attribute set to a value of "none" (if the contact is
offline, the contact's server MUST modify the roster item and send
that modified item the next time the contact requests the roster);
and (2) MUST also deliver the "unsubscribe" state change notification
to the contact:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@somedomain'
subscription='none'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
Saint-Andre & Miller Expires April 25, 2004 [Page 53]
Internet-Draft XMPP Instant Messaging October 2003
</iq>
<presence
from='user@somedomain'
to='contact@otherdomain'
type='unsubscribed'/>
Upon receiving the presence stanza of type "unavailable" addressed to
the contact, the contact's server MUST deliver the unavailable
presence to the user:
<presence
from='user@somedomain'
to='contact@otherdomain'
type='unavailable'/>
Note that when the user removes the contact from the user's roster,
the end state of the contact's roster is that the user is still in
the contact's roster with a subscription state of "none"; in order to
completely remove the roster item for the user, the contact needs to
also send a roster removal request.
9. Subscription States
This section provides detailed information about subscription states.
9.1 Defined States
There are nine possible subscription states, which are described here
from the user's perspective:
1. "None" = contact and user are not subscribed to each other, and
neither has requested a subscription from the other
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 responded yet
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 responded yet
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 responded yet, and user has sent contact a subscription
request but contact has not responded yet
5. "To" = user is subscribed to contact (one-way)
Saint-Andre & Miller Expires April 25, 2004 [Page 54]
Internet-Draft XMPP Instant Messaging October 2003
6. "To + Pending In" = user is subscribed to contact, and contact
has send user a subscription request but user has not responded
yet
7. "From" = contact is subscribed to user (one-way)
8. "From + Pending Out" = contact is subscribed to user, and user
has sent contact a subscription request but contact has not
responded yet
9. "Both" = user and contact are subscribed to each other (two-way)
9.2 Server Handling of Outbound Presence, Categorized by Subscription
State
This section defines how a server MUST handle an outbound presence
stanza of type "subscribe", "subscribed", "unsubscribe", or
"unsubscribed" (i.e., route it to the intended recipient and/or make
a change to the subscription state), categorized by the current
subscription state. The general rule is that a server MUST route the
stanza to the intended recipient if it would change the subscription
state, and MUST NOT route the stanza if it would not change the
subscription state. Detailed definitions are contained in the
following sections. Naturally, if the stanza changes the subscription
state, the server MUST change the subscription state in addition to
routing the subscription state.
9.2.1 Subscription State = None
+-------------------------------------------------------+
| STANZA TYPE | ROUTE? | NEW STATE |
+-------------------------------------------------------+
| subscribe | yes | "None + Pending Out" |
| subscribed | no | no state change |
| unsubscribe | no | no state change |
| unsubscribed | no | no state change |
+-------------------------------------------------------+
9.2.2 Subscription State = None + Pending Out
+-------------------------------------------------------+
| STANZA TYPE | ROUTE? | NEW STATE |
+-------------------------------------------------------+
| subscribe | no | no state change |
| subscribed | no | no state change |
| unsubscribe | yes | "None" |
Saint-Andre & Miller Expires April 25, 2004 [Page 55]
Internet-Draft XMPP Instant Messaging October 2003
| unsubscribed | no | no state change |
+-------------------------------------------------------+
9.2.3 Subscription State = None + Pending In
+-------------------------------------------------------+
| STANZA TYPE | ROUTE? | NEW STATE |
+-------------------------------------------------------+
| subscribe | yes | "None + Pending Out/In" |
| subscribed | yes | "From" |
| unsubscribe | no | no state change |
| unsubscribed | yes | "None" |
+-------------------------------------------------------+
9.2.4 Subscription State = None + Pending Out/In
+-------------------------------------------------------+
| STANZA TYPE | ROUTE? | NEW STATE |
+-------------------------------------------------------+
| subscribe | no | no state change |
| subscribed | yes | "From + Pending Out" |
| unsubscribe | yes | "None + Pending In" |
| unsubscribed | yes | "None + Pending Out" |
+-------------------------------------------------------+
9.2.5 Subscription State = To
+-------------------------------------------------------+
| STANZA TYPE | ROUTE? | NEW STATE |
+-------------------------------------------------------+
| subscribe | no | no state change |
| subscribed | no | no state change |
| unsubscribe | yes | "None" |
| unsubscribed | no | no state change |
+-------------------------------------------------------+
9.2.6 Subscription State = To + Pending In
+-------------------------------------------------------+
| STANZA TYPE | ROUTE? | NEW STATE |
+-------------------------------------------------------+
| subscribe | no | no state change |
| subscribed | yes | "Both" |
| unsubscribe | yes | "None + Pending In" |
Saint-Andre & Miller Expires April 25, 2004 [Page 56]
Internet-Draft XMPP Instant Messaging October 2003
| unsubscribed | yes | "To" |
+-------------------------------------------------------+
9.2.7 Subscription State = From
+-------------------------------------------------------+
| STANZA TYPE | ROUTE? | NEW STATE |
+-------------------------------------------------------+
| subscribe | yes | "From + Pending Out" |
| subscribed | no | no state change |
| unsubscribe | no | no state change |
| unsubscribed | yes | "None" |
+-------------------------------------------------------+
9.2.8 Subscription State = From + Pending Out
+-------------------------------------------------------+
| STANZA TYPE | ROUTE? | NEW STATE |
+-------------------------------------------------------+
| subscribe | no | no state change |
| subscribed | no | no state change |
| unsubscribe | yes | "From" |
| unsubscribed | yes | "None + Pending Out" |
+-------------------------------------------------------+
9.2.9 Subscription State = Both
+-------------------------------------------------------+
| STANZA TYPE | ROUTE? | NEW STATE |
+-------------------------------------------------------+
| subscribe | no | no state change |
| subscribed | no | no state change |
| unsubscribe | yes | "From" |
| unsubscribed | yes | "To" |
+-------------------------------------------------------+
9.3 Server Handling of Outbound Presence, Categorized by Presence Type
This section defines how a server MUST handle an outbound presence
stanza of type "subscribe", "subscribed", "unsubscribe", or
"unsubscribed" (i.e., route it to the intended recipient and/or make
a change to the subscription state), categorized by presence type.
Saint-Andre & Miller Expires April 25, 2004 [Page 57]
Internet-Draft XMPP Instant Messaging October 2003
9.3.1 Subscribe
+----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+----------------------------------------------------------------+
| "None" | yes | "None + Pending Out" |
| "None + Pending Out" | no | no state change |
| "None + Pending In" | yes | "None + Pending Out/In" |
| "None + Pending Out/In" | no | no state change |
| "To" | no | no state change |
| "To + Pending In" | no | no state change |
| "From" | yes | "From + Pending Out" |
| "From + Pending Out" | no | no state change |
| "Both" | no | no state change |
+----------------------------------------------------------------+
9.3.2 Subscribed
+----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+----------------------------------------------------------------+
| "None" | no | no state change |
| "None + Pending Out" | no | no state change |
| "None + Pending In" | yes | "From" |
| "None + Pending Out/In" | yes | "From + Pending Out" |
| "To" | no | no state change |
| "To + Pending In" | yes | "Both" |
| "From" | no | no state change |
| "From + Pending Out" | no | no state change |
| "Both" | no | no state change |
+----------------------------------------------------------------+
9.3.3 Unsubscribe
+----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+----------------------------------------------------------------+
| "None" | no | no state change |
| "None + Pending Out" | yes | "None" |
| "None + Pending In" | no | no state change |
| "None + Pending Out/In" | yes | "None + Pending In" |
| "To" | yes | "None" |
| "To + Pending In" | yes | "None + Pending In" |
| "From" | no | no state change |
| "From + Pending Out" | yes | "From" |
| "Both" | yes | "From" |
Saint-Andre & Miller Expires April 25, 2004 [Page 58]
Internet-Draft XMPP Instant Messaging October 2003
+----------------------------------------------------------------+
Note: When a user sends an outbound presence stanza of type
"unsubscribe" that results in a subscription state change, the
contact's server SHOULD auto-reply by sending a presence stanza of
type "unsubscribed" to the user on behalf of the contact and MUST
deliver that presence stanza to the contact.
9.3.4 Unsubscribed
+----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+----------------------------------------------------------------+
| "None" | no | no state change |
| "None + Pending Out" | no | no state change |
| "None + Pending In" | yes | "None" |
| "None + Pending Out/In" | yes | "None + Pending Out" |
| "To" | no | no state change |
| "To + Pending In" | yes | "To" |
| "From" | yes | "None" |
| "From + Pending Out" | yes | "None + Pending Out" |
| "Both" | yes | "To" |
+----------------------------------------------------------------+
9.4 Server Handling of Inbound Presence, Categorized by Subscription
State
This section defines how a server MUST handle an inbound presence
stanza of type "subscribe", "subscribed", "unsubscribe", or
"unsubscribed" (i.e., deliver it to the intended recipient and/or
make a change to the subscription state), categorized by subscription
state. (Note: some of the presence stanza types should never be
received as inbound stanzas, since the sender's server MUST NOT route
them to the intended recipient; however, these stanza types are
included for the sake of completeness.)
9.4.1 Subscription State = None
+--------------------------------------------------------+
| STANZA TYPE | DELIVER? | NEW STATE |
+--------------------------------------------------------+
| subscribe | yes | "None + Pending In" |
| subscribed | no | no state change |
| unsubscribe | no | no state change |
| unsubscribed | no | no state change |
+--------------------------------------------------------+
Saint-Andre & Miller Expires April 25, 2004 [Page 59]
Internet-Draft XMPP Instant Messaging October 2003
9.4.2 Subscription State = None + Pending Out
+--------------------------------------------------------+
| STANZA TYPE | DELIVER? | NEW STATE |
+--------------------------------------------------------+
| subscribe | yes | "None + Pending Out/In" |
| subscribed | yes | "To" |
| unsubscribe | no | no state change |
| unsubscribed | yes | "None" |
+--------------------------------------------------------+
9.4.3 Subscription State = None + Pending In
+--------------------------------------------------------+
| STANZA TYPE | DELIVER? | NEW STATE |
+--------------------------------------------------------+
| subscribe | no | no state change |
| subscribed | no | no state change |
| unsubscribe | yes | "None" |
| unsubscribed | no | no state change |
+--------------------------------------------------------+
9.4.4 Subscription State = None + Pending Out/In
+--------------------------------------------------------+
| STANZA TYPE | DELIVER? | NEW STATE |
+--------------------------------------------------------+
| subscribe | no | no state change |
| subscribed | yes | "To + Pending In" |
| unsubscribe | yes | "None + Pending Out" |
| unsubscribed | yes | "None + Pending In" |
+--------------------------------------------------------+
9.4.5 Subscription State = To
+--------------------------------------------------------+
| STANZA TYPE | DELIVER? | NEW STATE |
+--------------------------------------------------------+
| subscribe | yes | "To + Pending In" |
| subscribed | no | no state change |
| unsubscribe | no | no state change |
| unsubscribed | yes | "None" |
+--------------------------------------------------------+
Saint-Andre & Miller Expires April 25, 2004 [Page 60]
Internet-Draft XMPP Instant Messaging October 2003
9.4.6 Subscription State = To + Pending In
+--------------------------------------------------------+
| STANZA TYPE | DELIVER? | NEW STATE |
+--------------------------------------------------------+
| subscribe | no | no state change |
| subscribed | no | no state change |
| unsubscribe | yes | "To" |
| unsubscribed | yes | "None + Pending In" |
+--------------------------------------------------------+
9.4.7 Subscription State = From
+--------------------------------------------------------+
| STANZA TYPE | DELIVER? | NEW STATE |
+--------------------------------------------------------+
| subscribe | no | no state change |
| subscribed | no | no state change |
| unsubscribe | yes | "None" |
| unsubscribed | no | no state change |
+--------------------------------------------------------+
9.4.8 Subscription State = From + Pending Out
+--------------------------------------------------------+
| STANZA TYPE | DELIVER? | NEW STATE |
+--------------------------------------------------------+
| subscribe | no | no state change |
| subscribed | yes | "Both" |
| unsubscribe | yes | "None + Pending Out" |
| unsubscribed | yes | "From" |
+--------------------------------------------------------+
9.4.9 Subscription State = Both
+--------------------------------------------------------+
| STANZA TYPE | DELIVER? | NEW STATE |
+--------------------------------------------------------+
| subscribe | no | no state change |
| subscribed | no | no state change |
| unsubscribe | yes | "To" |
| unsubscribed | yes | "From" |
+--------------------------------------------------------+
Saint-Andre & Miller Expires April 25, 2004 [Page 61]
Internet-Draft XMPP Instant Messaging October 2003
9.5 Server Handling of Inbound Presence, Categorized by Presence Type
This section defines how a server MUST handle an inbound presence
stanza of type "subscribe", "subscribed", "unsubscribe", or
"unsubscribed" (i.e., deliver it to the intended recipient and/or
make a change to the subscription state), categorized by presence
type.
9.5.1 Subscribe
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | yes | "None + Pending In" |
| "None + Pending Out" | yes | "None + Pending Out/In" |
| "None + Pending In" | no | no state change |
| "None + Pending Out/In" | no | no state change |
| "To" | yes | "To + Pending In" |
| "To + Pending In" | no | no state change |
| "From" | no | no state change |
| "From + Pending Out" | no | no state change |
| "Both" | no | no state change |
+------------------------------------------------------------------+
9.5.2 Subscribed
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | no | no state change |
| "None + Pending Out" | yes | "To" |
| "None + Pending In" | no | no state change |
| "None + Pending Out/In" | yes | "To + Pending In" |
| "To" | no | no state change |
| "To + Pending In" | no | no state change |
| "From" | no | no state change |
| "From + Pending Out" | yes | "Both" |
| "Both" | no | no state change |
+------------------------------------------------------------------+
9.5.3 Unsubscribe
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | no | no state change |
Saint-Andre & Miller Expires April 25, 2004 [Page 62]
Internet-Draft XMPP Instant Messaging October 2003
| "None + Pending Out" | no | no state change |
| "None + Pending In" | yes | "None" |
| "None + Pending Out/In" | yes | "None + Pending Out" |
| "To" | no | no state change |
| "To + Pending In" | yes | "To" |
| "From" | yes | "None" |
| "From + Pending Out" | yes | "None + Pending Out |
| "Both" | yes | "To" |
+------------------------------------------------------------------+
9.5.4 Unsubscribed
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | no | no state change |
| "None + Pending Out" | yes | "None" |
| "None + Pending In" | no | no state change |
| "None + Pending Out/In" | yes | "None + Pending In" |
| "To" | yes | "None" |
| "To + Pending In" | yes | "None + Pending In" |
| "From" | no | no state change |
| "From + Pending Out" | yes | "From" |
| "Both" | yes | "From" |
+------------------------------------------------------------------+
9.6 Server Delivery and Client Acknowledgement of Subscription State
Change Notifications
When a server receives an inbound presence stanza of type
"subscribe", "subscribed", "unsubscribe", or "unsubscribed" that
consists of a subscription state change notification, in addition to
sending the appropriate roster push (or updated roster when the
roster is next requested), it MUST deliver the notification to the
intended recipient at least once. A server MAY require the recipient
to acknowledge receipt of the all state change notifications (and
MUST require acknowledgement in the case of subscription requests,
i.e., presence stanzas of type "subscribe"). In order to require
acknowledgement, a server SHOULD send the notification to the
recipient each time the recipient logs in, until the recipient
acknowledges receipt of the notification by "affirming" or "denying"
the notification, as shown in the following table:
+--------------------------------------------------+
| NOTIFICATION | ACCEPT | DENY |
+--------------------------------------------------+
Saint-Andre & Miller Expires April 25, 2004 [Page 63]
Internet-Draft XMPP Instant Messaging October 2003
| subscribe | subscribed | unsubscribed |
| subscribed | subscribe | unsubscribe |
| unsubscribe | unsubscribed | subscribed |
| unsubscribed | unsubscribe | subscribe |
+--------------------------------------------------+
Obviously, given the foregoing subscription state charts, some of the
acknowledgement stanzas will be routed to the contact and result in
subscription state changes, while others will not. However, any such
stanzas MUST result in the server's no longer sending the
subscription state notification to the user.
Because a user's server MUST automatically generate outbound presence
stanzas of type "unsubscribe" and "unsubscribed" upon receiving a
roster set with the 'subscription' attribute set to a value of
"remove" (see Removing a Roster Item and Cancelling All Subscriptions
(Section 8.6)) the server MUST treat a roster remove request as
equivalent to sending those presence stanzas for purposes of
determining whether to continue sending subscription state change
notifications of type "subscribe" or "subscribed" to the user.
10. Blocking Communication
Most instant messaging systems have found it necessary to implement
some method for users to block communications from particular other
users (this is also required by sections 5.1.5, 5.1.15, 5.3.2, and
5.4.10 of RFC 2779 [2]). In XMPP this is done using the
'jabber:iq:privacy' namespace by managing one's privacy lists.
Server-side privacy lists enable successful completion of the
following use cases:
o Retrieving one's privacy lists.
o Adding, removing, and editing one's privacy lists.
o Setting, changing, or declining active lists.
o Setting, changing, or declining the default list (i.e., the list
that is active by default).
o Allowing or blocking messages based on JID, group, or subscription
type (or globally).
o Allowing or blocking inbound presence notifications based on JID,
group, or subscription type (or globally).
o Allowing or blocking outbound presence notifications based on JID,
Saint-Andre & Miller Expires April 25, 2004 [Page 64]
Internet-Draft XMPP Instant Messaging October 2003
group, or subscription type (or globally).
o Allowing or blocking IQs based on JID, group, or subscription type
(or globally).
o Allowing or blocking all communications based on JID, group, or
subscription type (or globally).
Note: presence notifications do not include presence subscriptions,
only presence information that is broadcasted to entities that are
subscribed to a user's presence information. Thus this includes
presence stanzas with no 'type' attribute or of type='unavailable'
only.
10.1 Syntax and Semantics
A user MAY define one or more privacy lists, which are stored by the
user's server. Each <list/> element contains one or more rules in the
form of <item/> elements, and each <item/> element uses attributes to
define a privacy rule type, a specific value to which the rules
applies, the relevant action, and the place of the item in the
processing order.
The syntax is as follows:
<iq>
<query xmlns='jabber:iq:privacy'>
<list name='foo'>
<item
type='[jid|group|subscription]'
value='bar'
action='[allow|deny]'
order='unsignedInt'>
[<message/>]
[<presence-in/>]
[<presence-out/>]
[<iq/>]
</item>
</list>
</query>
</iq>
If the type is "jid", then the 'value' attribute MUST contain a valid
Jabber ID. JIDs are matched in the following order: <user@domain/
resource>, then <user@domain>, then <domain/resource>, then <domain>.
If the value is <user@domain>, then any connected resource for that
user@domain matches. If the value is <domain/resource>, then only
that resource matches. If the value is <domain>, then any user@domain
Saint-Andre & Miller Expires April 25, 2004 [Page 65]
Internet-Draft XMPP Instant Messaging October 2003
(or subdomain) matches.
If the type is "group", then the 'value' attribute SHOULD contain the
name of a group in the user's roster. (If a client attempts to
update, create, or delete a list item with a group that is not in the
user's roster, the server SHOULD return to the client an
<item-not-found/> stanza error.)
If the type is "subscription", then the 'value' attribute MUST be one
of "both", "to", "from", or "none" as defined under Roster Syntax and
Semantics (Section 7.1).
If no 'type' attribute is included, the rule provides the
"fall-through" case.
The 'action' attribute MUST be included and its value MUST be either
"accept" or "deny".
The 'order' attribute MUST be included and its value MUST be a
non-negative integer that is unique among all items in the list. (If
a client attempts to create or update a list with non-unique order
values, the server MUST return to the client a <bad-request/> stanza
error.)
The <item/> element MAY contain one or more child elements that
enable an entity to specify more granular control over which kinds of
stanzas are to be blocked (i.e., rather than blocking all stanzas).
The allowable child elements are:
o <message/> -- blocks incoming message stanzas
o <iq/> -- blocks incoming IQ stanzas
o <presence-in/> -- blocks incoming presence notifications
o <presence-out/> -- blocks outgoing presence notifications
Within the 'jabber:iq:privacy' namespace, the <query/> child of a
client-generated IQ stanza of type "set" MUST NOT include more than
one child element (i.e., the stanza must contain only one <active/>
element, one <default/> element, or one <list/> element); if a client
violates this rule, the server MUST return to the client a
<bad-request/> stanza error.
When a client adds or updates a privacy list, the <list/> element
SHOULD contain at least one <item/> child element; when a client
removes a privacy list, the <list/> element SHOULD contain no <item/>
child element.
Saint-Andre & Miller Expires April 25, 2004 [Page 66]
Internet-Draft XMPP Instant Messaging October 2003
When a client updates a privacy list, it must include all of the
desired items (i.e., not a "delta").
10.2 Business Rules
1. If there is an active list set for a session, it affects only the
session for which it is activated, and only for the duration of
the session. The server MUST apply the active list only and MUST
NOT apply the default list.
2. The default list applies to the user as a whole, and is processed
if there is no active list set for the target session/resource to
which a stanza is addressed, or if there are no current sessions
for the user.
3. If there is no active list set for a session (or there are no
current sessions for the user), and there is no default list,
then all stanzas SHOULD BE accepted or appropriately processed by
the server on behalf of the user.
4. Privacy lists MUST be the first rule applied by a server,
superseding (1) the routing and delivery rules specified in
Server Rules for Handling XML Stanzas (Section 14), and (2) the
handling of subscription-related presence stanzas (and
corresponding generation of roster pushes) specified in
Integration of Roster Items and Presence Subscriptions (Section
8).
5. The order in which privacy list items are processed by the server
is important. List items MUST be processed in ascending order
determined by the integer values of the 'order' attribute for
each <item/>.
6. As soon as a stanza is matched against a privacy list, the server
SHOULD appropriately handle the stanza and cease processing.
7. If no fall-through item is provided in a list, the fall-through
action is assumed to be "accept".
8. If a user updates the definition for an active list, subsequent
processing based on that active list MUST use the updated
definition (for all resources to which that active list currently
applies).
9. If a change to the subscription state or roster group of a roster
item defined in an active or default list occurs during a user's
session, subsequent processing based on that list MUST take into
account the changed state or group (for all resources to which
Saint-Andre & Miller Expires April 25, 2004 [Page 67]
Internet-Draft XMPP Instant Messaging October 2003
that list currently applies).
10.3 Retrieving One's Privacy Lists
Example: Client requests names of privacy lists from server:
<iq from='romeo@example.org/orchard' type='get' id='getlist1'>
<query xmlns='jabber:iq:privacy'/>
</iq>
Example: Server sends names of privacy lists to client, preceded by
active list and default list:
<iq type='result' id='getlist1' to='romeo@example.net/orchard'>
<query xmlns='jabber:iq:privacy'>
<active name='private'/>
<default name='public'/>
<list name='public'/>
<list name='private'/>
<list name='special'/>
</query>
</iq>
Example: Client requests a privacy list from server:
<iq from='romeo@example.org/orchard' type='get' id='getlist2'>
<query xmlns='jabber:iq:privacy'>
<list name='public'/>
</query>
</iq>
Example: Server sends a privacy list to client:
<iq type='result' id='getlist2' to='romeo@example.net/orchard'>
<query xmlns='jabber:iq:privacy'>
<list name='public'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='1'/>
<item action='allow' order='2'/>
</list>
</query>
</iq>
Example: Client requests another privacy list from server:
Saint-Andre & Miller Expires April 25, 2004 [Page 68]
Internet-Draft XMPP Instant Messaging October 2003
<iq from='romeo@example.org/orchard' type='get' id='getlist3'>
<query xmlns='jabber:iq:privacy'>
<list name='private'/>
</query>
</iq>
Example: Server sends another privacy list to client:
<iq type='result' id='getlist3' to='romeo@example.net/orchard'>
<query xmlns='jabber:iq:privacy'>
<list name='private'>
<item type='subscription'
value='both'
action='allow'
order='10'/>
<item action='deny' order='15'/>
</list>
</query>
</iq>
Example: Client requests yet another privacy list from server:
<iq from='romeo@example.org/orchard' type='get' id='getlist4'>
<query xmlns='jabber:iq:privacy'>
<list name='special'/>
</query>
</iq>
Example: Server sends yet another privacy list to client:
<iq type='result' id='getlist4' to='romeo@example.net/orchard'>
<query xmlns='jabber:iq:privacy'>
<list name='special'>
<item type='jid'
value='juliet@example.com'
action='allow'
order='6'/>
<item type='jid'
value='benvolio@example.org'
action='allow'
order='7'/>
<item type='jid'
value='mercutio@example.org'
action='allow'
order='42'/>
<item action='deny' order='666'/>
</list>
</query>
Saint-Andre & Miller Expires April 25, 2004 [Page 69]
Internet-Draft XMPP Instant Messaging October 2003
</iq>
In this example, the user has three lists: (1) 'public', which allows
communications from everyone except one specific entity (this is the
default list); (2) 'private', which allows communications only with
contacts who have a bidirectional subscription with the user (this is
the active list); and (3) 'special', which allows communications only
with three specific entities.
If the user attempts to retrieve a list but a list by that name does
not exist, the server MUST return an <item-not-found/> stanza error
to the user:
Example: Client attempts to retrieve non-existent list:
<iq to='romeo@example.org/orchard' type='error' id='getlist5'>
<query xmlns='jabber:iq:privacy'>
<list name='The Empty Set'/>
</query>
<error type='cancel'>
<item-not-found
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
The user is allowed to retrieve only one list at a time. If the user
attempts to retrieve more than one list in the same request, the
server MUST return a <bad request/> stanza error to the user:
Example: Client attempts to retrieve more than one list:
<iq to='romeo@example.org/orchard' type='error' id='getlist6'>
<query xmlns='jabber:iq:privacy'>
<list name='public'/>
<list name='private'/>
<list name='special'/>
</query>
<error type='modify'>
<bad-request
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
10.4 Managing Active Lists
In order to set or change the active list currently being applied by
the server, the user MUST send an IQ stanza of type "set" with a
Saint-Andre & Miller Expires April 25, 2004 [Page 70]
Internet-Draft XMPP Instant Messaging October 2003
<query/> element qualified by the 'jabber:iq:privacy' namespace that
contains an empty <active/> child element possessing a 'name'
attribute whose value is set to the desired list name.
Example: Client requests change of active list:
<iq from='romeo@example.org/orchard' type='set' id='active1'>
<query xmlns='jabber:iq:privacy'>
<active name='special'/>
</query>
</iq>
The server MUST activate and apply the requested list before sending
the result back to the client.
Example: Server acknowledges success of active list change:
<iq type='result' id='active1' to='juliet@example.com/balcony'/>
If the user attempts to set an active list but a list by that name
does not exist, the server MUST return an <item-not-found/> stanza
error to the user:
Example: Client attempts to set a non-existent list as active:
<iq to='romeo@example.org/orchard' type='error' id='active2'>
<query xmlns='jabber:iq:privacy'>
<active name='The Empty Set'/>
</query>
<error type='cancel'>
<item-not-found
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
In order to decline the use of any active list, the user MUST send an
empty <active/> element with no name.
Example: Client declines the use of active lists:
<iq from='romeo@example.org/orchard' type='set' id='active2'>
<query xmlns='jabber:iq:privacy'>
<active/>
</query>
</iq>
Saint-Andre & Miller Expires April 25, 2004 [Page 71]
Internet-Draft XMPP Instant Messaging October 2003
10.5 Managing the Default List
In order to change its default list, the user MUST send an IQ stanza
of type "set" with a <query/> element qualified by the
'jabber:iq:privacy' namespace that contains an empty <default/> child
element possessing a 'name' attribute whose value is set to the
desired list name.
Example: Client requests change of default list:
<iq from='romeo@example.org/orchard' type='set' id='default1'>
<query xmlns='jabber:iq:privacy'>
<default name='special'/>
</query>
</iq>
Example: Server acknowledges success of default list change:
<iq type='result' id='default1' to='juliet@example.com/balcony'/>
If the user attempts to set a default list but a list by that name
does not exist, the server MUST return an <item-not-found/> stanza
error to the user:
Example: Client attempts to set a non-existent list as default:
<iq to='romeo@example.org/orchard' type='error' id='default2'>
<query xmlns='jabber:iq:privacy'>
<default name='The Empty Set'/>
</query>
<error type='cancel'>
<item-not-found
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
In order to decline the use of a default list (i.e., to use the
domain's stanza routing rules at all times), the user MUST send an
empty <default/> element with no name.
Example: Client declines the use of the default list:
<iq from='romeo@example.org/orchard' type='set' id='default2'>
<query xmlns='jabber:iq:privacy'>
<default/>
</query>
</iq>
Saint-Andre & Miller Expires April 25, 2004 [Page 72]
Internet-Draft XMPP Instant Messaging October 2003
10.6 Editing a Privacy List
In order to edit a privacy list, the user MUST send an IQ stanza of
type "set" with a <query/> element qualified by the
'jabber:iq:privacy' namespace that contains one <list/> child element
possessing a 'name' attribute whose value is set to the list name the
user would like to edit. The <list/> element MUST contain one or more
<item/> elements, which specify the user's desired changes to the
list by including all elements in the list (not the "delta").
Example: Client edits a privacy list:
<iq from='romeo@example.org/orchard' type='set' id='edit1'>
<query xmlns='jabber:iq:privacy'>
<list name='public'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='3'/>
<item type='jid'
value='paris@example.org'
action='deny'
order='5'/>
<item action='allow' order='68'/>
</list>
</query>
</iq>
Example: Server acknowledges success of list edit:
<iq type='result' id='edit1' to='juliet@example.com/balcony'/>
Note: The value of the 'order' attribute for any given item is not
fixed. Thus in the foregoing example if the user would like to add 4
items between the "tybalt@example.com" item and the
"paris@example.org" item, the user's client MUST renumber the
relevant items before submitting the list to the server.
10.7 Adding a New Privacy List
The same protocol used to edit an existing list is used to create a
new list. If the list name matches that of an existing list, the
request to add a new list will overwrite the old one.
10.8 Removing a Privacy List
In order to remove a privacy list, the user MUST send an IQ stanza of
type "set" with a <query/> element qualified by the
Saint-Andre & Miller Expires April 25, 2004 [Page 73]
Internet-Draft XMPP Instant Messaging October 2003
'jabber:iq:privacy' namespace that contains one empty <list/> child
element possessing a 'name' attribute whose value is set to the list
name the user would like to remove.
Example: Client removes a privacy list:
<iq from='romeo@example.org/orchard' type='set' id='remove1'>
<query xmlns='jabber:iq:privacy'>
<list name='private'/>
</query>
</iq>
Example: Server acknowledges success of list removal:
<iq type='result' id='remove1' to='juliet@example.com/balcony'/>
If a user attempts to remove an active list or the default list, the
server MUST return a <conflict/> stanza error to the user. The user
MUST first set another list to active or default before removing it.
If the user attempts to remove a list but a list by that name does
not exist, the server MUST return an <item-not-found/> stanza error
to the user:
If the user attempts to remove more than one list in the same
request, the server MUST return a <bad request/> stanza error to the
user.
10.9 Blocking Messages
Server-side privacy lists enable a user to block incoming messages
from other users based on the other user's JID, roster group, or
subscription status (or globally). The following examples illustrate
the protocol.
Example: User blocks based on JID:
<iq from='romeo@example.org/orchard' type='set' id='msg1'>
<query xmlns='jabber:iq:privacy'>
<list name='message-jid-example'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='3'>
<message/>
</item>
</list>
</query>
Saint-Andre & Miller Expires April 25, 2004 [Page 74]
Internet-Draft XMPP Instant Messaging October 2003
</iq>
As a result of creating and applying the foregoing list, the user
will not receive messages from the user with the specified JID.
Example: User blocks based on roster group:
<iq from='romeo@example.org/orchard' type='set' id='msg2'>
<query xmlns='jabber:iq:privacy'>
<list name='message-group-example'>
<item type='group'
value='Enemies'
action='deny'
order='4'>
<message/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive messages from any users in the specified roster
group.
Example: User blocks based on subscription type:
<iq from='romeo@example.org/orchard' type='set' id='msg3'>
<query xmlns='jabber:iq:privacy'>
<list name='message-sub-example'>
<item type='subscription'
value='none'
action='deny'
order='5'>
<message/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive messages from any users with the specified
subscription type.
Example: User blocks globally:
<iq from='romeo@example.org/orchard' type='set' id='msg4'>
<query xmlns='jabber:iq:privacy'>
<list name='message-global-example'>
Saint-Andre & Miller Expires April 25, 2004 [Page 75]
Internet-Draft XMPP Instant Messaging October 2003
<item action='deny' order='6'>
<message/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive messages from any other users.
10.10 Blocking Inbound Presence Notifications
Server-side privacy lists enable a user to block incoming presence
notifications from other users based on the other user's JID, roster
group, or subscription status (or globally). The following examples
illustrate the protocol.
Note: presence notifications do not include presence subscriptions,
only presence information that is broadcasted to the user because the
user previously subscribed to a contact's presence information. Thus
this includes presence stanzas with no 'type' attribute or of
type='unavailable' only.
Example: User blocks based on JID:
<iq from='romeo@example.org/orchard' type='set' id='presin1'>
<query xmlns='jabber:iq:privacy'>
<list name='presin-jid-example'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='7'>
<presence-in/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive presence notifications from the user with the
specified JID.
Example: User blocks based on roster group:
<iq from='romeo@example.org/orchard' type='set' id='presin2'>
<query xmlns='jabber:iq:privacy'>
<list name='presin-group-example'>
<item type='group'
Saint-Andre & Miller Expires April 25, 2004 [Page 76]
Internet-Draft XMPP Instant Messaging October 2003
value='Enemies'
action='deny'
order='8'>
<presence-in/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive presence notifications from any users in the
specified roster group.
Example: User blocks based on subscription type:
<iq from='romeo@example.org/orchard' type='set' id='presin3'>
<query xmlns='jabber:iq:privacy'>
<list name='presin-sub-example'>
<item type='subscription'
value='to'
action='deny'
order='9'>
<presence-in/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive presence notifications from any users with the
specified subscription type.
Example: User blocks globally:
<iq from='romeo@example.org/orchard' type='set' id='presin4'>
<query xmlns='jabber:iq:privacy'>
<list name='presin-global-example'>
<item action='deny' order='11'>
<presence-in/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive presence notifications from any other users.
Saint-Andre & Miller Expires April 25, 2004 [Page 77]
Internet-Draft XMPP Instant Messaging October 2003
10.11 Blocking Outbound Presence Notifications
Server-side privacy lists enable a user to block outgoing presence
notifications to other users based on the other user's JID, roster
group, or subscription status (or globally). The following examples
illustrate the protocol.
Note: presence notifications do not include presence subscriptions,
only presence information that is broadcasted to contacts because
those contacts previously subscribed to the user's presence
information. Thus this includes presence stanzas with no 'type'
attribute or of type='unavailable' only.
Example: User blocks based on JID:
<iq from='romeo@example.org/orchard' type='set' id='presout1'>
<query xmlns='jabber:iq:privacy'>
<list name='presout-jid-example'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='13'>
<presence-out/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not send presence notifications to the user with the specified
JID.
Example: User blocks based on roster group:
<iq from='romeo@example.org/orchard' type='set' id='presout2'>
<query xmlns='jabber:iq:privacy'>
<list name='presout-group-example'>
<item type='group'
value='Enemies'
action='deny'
order='15'>
<presence-out/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
Saint-Andre & Miller Expires April 25, 2004 [Page 78]
Internet-Draft XMPP Instant Messaging October 2003
will not send presence notifications to any users in the specified
roster group.
Example: User blocks based on subscription type:
<iq from='romeo@example.org/orchard' type='set' id='presout3'>
<query xmlns='jabber:iq:privacy'>
<list name='presout-sub-example'>
<item type='subscription'
value='from'
action='deny'
order='17'>
<presence-out/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not send presence notifications to any users with the specified
subscription type.
Example: User blocks globally:
<iq from='romeo@example.org/orchard' type='set' id='presout4'>
<query xmlns='jabber:iq:privacy'>
<list name='presout-global-example'>
<item action='deny' order='23'>
<presence-out/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not send presence notifications to any other users.
10.12 Blocking IQs
Server-side privacy lists enable a user to block incoming IQ stanzas
from other users based on the other user's JID, roster group, or
subscription status (or globally). The following examples illustrate
the protocol.
Example: User blocks based on JID:
<iq from='romeo@example.org/orchard' type='set' id='iq1'>
<query xmlns='jabber:iq:privacy'>
Saint-Andre & Miller Expires April 25, 2004 [Page 79]
Internet-Draft XMPP Instant Messaging October 2003
<list name='iq-jid-example'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='29'>
<iq/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive IQ stanzas from the user with the specified JID.
Example: User blocks based on roster group:
<iq from='romeo@example.org/orchard' type='set' id='iq2'>
<query xmlns='jabber:iq:privacy'>
<list name='iq-group-example'>
<item type='group'
value='Enemies'
action='deny'
order='31'>
<iq/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive IQ stanzas from any users in the specified roster
group.
Example: User blocks based on subscription type:
<iq from='romeo@example.org/orchard' type='set' id='iq3'>
<query xmlns='jabber:iq:privacy'>
<list name='iq-sub-example'>
<item type='subscription'
value='none'
action='deny'
order='17'>
<iq/>
</item>
</list>
</query>
</iq>
Saint-Andre & Miller Expires April 25, 2004 [Page 80]
Internet-Draft XMPP Instant Messaging October 2003
As a result of creating and applying the foregoing list, the user
will not receive IQ stanzas from any users with the specified
subscription type.
Example: User blocks globally:
<iq from='romeo@example.org/orchard' type='set' id='iq4'>
<query xmlns='jabber:iq:privacy'>
<list name='iq-global-example'>
<item action='deny' order='1'>
<iq/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive IQ stanzas from any other users.
10.13 Blocking All Communication
Server-side privacy lists enable a user to block all stanzas from and
to other users based on the other user's JID, roster group, or
subscription status (or globally). Note that this includes
subscription-related presence stanzas, which are excluded by Blocking
Inbound Presence Notifications (Section 10.10). The following
examples illustrate the protocol.
Example: User blocks based on JID:
<iq from='romeo@example.org/orchard' type='set' id='all1'>
<query xmlns='jabber:iq:privacy'>
<list name='all-jid-example'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='23'/>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive any communications from, nor send any stanzas to,
the user with the specified JID.
Example: User blocks based on roster group:
<iq from='romeo@example.org/orchard' type='set' id='all2'>
Saint-Andre & Miller Expires April 25, 2004 [Page 81]
Internet-Draft XMPP Instant Messaging October 2003
<query xmlns='jabber:iq:privacy'>
<list name='all-group-example'>
<item type='group'
value='Enemies'
action='deny'
order='13'/>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive any communications from, nor send any stanzas to,
any users in the specified roster group.
Example: User blocks based on subscription type:
<iq from='romeo@example.org/orchard' type='set' id='all3'>
<query xmlns='jabber:iq:privacy'>
<list name='all-sub-example'>
<item type='subscription'
value='none'
action='deny'
order='11'/>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive any communications from, nor send any stanzas to,
any users with the specified subscription type.
Example: User blocks globally:
<iq from='romeo@example.org/orchard' type='set' id='all4'>
<query xmlns='jabber:iq:privacy'>
<list name='all-global-example'>
<item action='deny' order='7'/>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive any communications from, nor send any stanzas to,
any other users.
10.14 Blocked Entity Attempts to Communicate with User
If a blocked entity attempts to send message or presence stanzas to
Saint-Andre & Miller Expires April 25, 2004 [Page 82]
Internet-Draft XMPP Instant Messaging October 2003
the user, the user's server SHOULD silently drop the stanza and MUST
NOT return an error to the sending entity.
If a blocked entity attempts to send an IQ stanza of type "get" or
"set" to the user, the user's server MUST return to the sending
entity a <feature-not-implemented/> stanza error, since this is the
standard error code sent from a client that does not understand the
namespace of an IQ get or set. IQ stanzas of other types SHOULD be
silently dropped by the server.
Example: Blocked entity attempts to send IQ get:
<iq type='get'
to='romeo@example.net'
from='tybalt@example.com/pda'
id='probing1'>
<query xmlns='jabber:iq:version'/>
</iq>
Example: Server returns error to blocked entity:
<iq type='error'
from='romeo@example.net'
to='tybalt@example.com/pda'
id='probing1'>
<query xmlns='jabber:iq:version'/>
<error type='cancel'>
<feature-not-implemented
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
10.15 Higher-Level Heuristics
When building a representation of a higher-level privacy heuristic, a
client SHOULD use the simplest possible representation.
For example, the heuristic "block all communications with any user
not in my roster" could be constructed in any of the following ways:
o allow communications from all JIDs in my roster (i.e., listing
each JID as a separate list item), but block communications with
everyone else
o allow communications from any user who is in one of the groups
that make up my roster (i.e., listing each group as a separate
list item), but block communications from everyone else
Saint-Andre & Miller Expires April 25, 2004 [Page 83]
Internet-Draft XMPP Instant Messaging October 2003
o allow communications from any user with whom I have a subscription
of 'both' or 'to' or 'from' (i.e., listing each subscription value
separately), but block communications from everyone else
o block communications from anyone whose subscription state is
'none'
The final representation is the simplest and SHOULD be used; here is
the XML that would be sent in this case:
<iq type='set' id='heuristic1'>
<query xmlns='jabber:iq:privacy'>
<list name='heuristic-example'>
<item type='subscription'
value='none'
action='deny'
order='437'/>
</list>
</query>
</iq>
11. IANA Considerations
For a number of related IANA considerations, refer to the relevant
section of XMPP Core [1].
11.1 XML Namespace Name for Session Data
A URN sub-namespace for session-related data in the Extensible
Messaging and Presence Protocol (XMPP) is defined as follows.
URI: urn:ietf:params:xml:ns:xmpp-session
Specification: [RFCXXXX]
Description: This is the XML namespace name for session-related data
in the Extensible Messaging and Presence Protocol (XMPP) as
defined by [RFCXXXX].
Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
12. Internationalization Considerations
For internationalization considerations, refer to the relevant
section of XMPP Core [1].
Saint-Andre & Miller Expires April 25, 2004 [Page 84]
Internet-Draft XMPP Instant Messaging October 2003
13. Security Considerations
Core security considerations for XMPP are defined in the relevant
section of XMPP Core [1].
Additional considerations that apply only to instant messaging and
presence applications of XMPP are defined in several places within
this memo; specifically:
o When a server processes a stanza of any kind whose intended
recipient is a user associated with one of the server's hostnames,
the server MUST first apply any privacy rules (Section 10) that
are in force (see Server Rules for Handling XML Stanzas (Section
14)).
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
information if the sender is a user who is not authorized to
receive that information as determined by presence subscriptions
(see Client and Server Presence Responsibilities (Section 5.1)).
o When a server processes an outbound presence stanza with no type
or of type "unavailable", it MUST follow the rules defined under
Client and Server Presence Responsibilities (Section 5.1) in order
to ensure that such presence information is not broadcasted to
entities that are not authorized to know such information.
14. Server Rules for Handling XML Stanzas
Basic routing and delivery rules for servers are defined in XMPP Core
[1]. This section defines additional rules for XMPP-compliant instant
messaging and presence servers.
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute of a stanza matches the hostname of the server
itself and the JID contained in the 'to' attribute is of the form
<user@somedomain> or <user@somedomain/resource>, the server MUST
first apply any privacy rules (Section 10) that are in force. If
privacy rules allow the stanza, it SHOULD be routed or delivered to
the intended recipient of the stanza as represented by the JID
contained in the 'to' attribute. The following additional rules apply
to instant messaging and presence applications, over and above those
defined in XMPP Core [1]:
1. If the JID is of the form <user@domain/resource> and an available
resource matches the full JID, the recipient's server MUST
Saint-Andre & Miller Expires April 25, 2004 [Page 85]
Internet-Draft XMPP Instant Messaging October 2003
deliver the stanza to that resource.
2. If the JID is of the form <user@domain/resource> and no available
resources match the full JID, the recipient's server (a) SHOULD
silently ignore the stanza (i.e., neither deliver it nor return
an error) if it is a presence stanza, (b) MUST return a
<service-unavailable/> stanza error to the sender if it is an IQ
stanza, and (c) MUST treat the stanza as if it were addressed to
<user@domain> if it is a message stanza.
3. If the JID is of the form <user@somedomain> and there is at least
one available resource available for the user, the recipient's
server MUST follow these rules:
1. For message stanzas, the server SHOULD deliver the stanza to
the highest-priority available resource (if the resource did
not provide a value for the <priority/> element, the server
SHOULD consider it to have provided a value of zero). If two
resources have the same priority, the server MAY use some
other rule (e.g., most recent connect time, most recent
activity time, or highest availability as determined by some
hierarchy of <show/> values) to choose between them. However,
the server MUST NOT deliver the stanza to an available
resource with a negative priority.
2. For presence stanzas other than those of type "probe", the
server MUST deliver the stanza to all available resources,
except that the server MUST NOT deliver the stanza to an
available resource that provided a negative value for the
<priority/> element; for presence probes, the server SHOULD
reply based on the rules defined in Client and Server
Presence Responsibilities (Section 5.1).
3. For IQ stanzas, 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 available resources.
Specifically, if the semantics of the qualifying namespace
define a reply that the server can provide, the server MUST
reply to the stanza on behalf of the user; if not, the server
MUST reply with a <service-unavailable/> stanza error.
4. If the JID is of the form <user@somedomain> and there are no
available resources associated with the user, how the stanza is
handled depends on the stanza type:
1. For presence stanzas of type "subscribe", the server MUST
maintain a record of the stanza and deliver it when the user
next becomes available, as specified under Client and Server
Saint-Andre & Miller Expires April 25, 2004 [Page 86]
Internet-Draft XMPP Instant Messaging October 2003
Presence Responsibilities (Section 5.1).
2. For all other presence stanzas, the server SHOULD silently
ignore the stanza by not storing it for later delivery or
replying to it on behalf of the user.
3. For message stanzas, the server MAY choose to store the
stanza on behalf of the user and deliver it when the user
next becomes available. However, if offline message storage
is not enabled, the server MUST return to the sender a
<service-unavailable/> stanza error. (Note: offline message
storage is not defined in XMPP since it strictly is a matter
of implementation and service provisioning.)
4. For IQ stanzas, 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, the server MUST reply to the
stanza on behalf of the user; if not, the server MUST reply
with a <service-unavailable/> stanza error.
15. Compliance Requirements
This section summarizes the specific aspects of the Extensible
Messaging and Presence Protocol that MUST be supported by instant
messaging servers and clients in order to be considered compliant
implementations. All such applications MUST comply with the
requirements specified in XMPP Core [1]. The text in this section
specifies additional compliance requirements for instant messaging
servers and clients; note well that the requirements described here
supplement but do not supersede the core requirements.
15.1 Servers
In addition to core server compliance requirements, an instant
messaging and presence server MUST additionally support the following
IM-related protocols:
o All server-related instant messaging syntax and semantics defined
in this document, including presence broadcast on behalf of
clients, presence subscriptions, roster storage and manipulation,
privacy rules, and IM-specific routing and delivery rules
15.2 Clients
In addition to core client compliance requirements, an instant
Saint-Andre & Miller Expires April 25, 2004 [Page 87]
Internet-Draft XMPP Instant Messaging October 2003
messaging client MUST additionally support the following IM-related
protocols:
o Generation and handling 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
o All client-related instant messaging syntax and semantics defined
in this document, including presence subscriptions, roster
management, and privacy rules
o End-to-end object encryption as defined in XMPP e2e [6]
Normative References
[1] Saint-Andre, P. and J. Miller, "XMPP Core",
draft-ietf-xmpp-core-19 (work in progress), October 2003.
[2] Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging /
Presence Protocol Requirements", RFC 2779, February 2000.
[3] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
"Extensible Markup Language (XML) 1.0 (2nd ed)", W3C REC-xml,
October 2000, <http://www.w3.org/TR/REC-xml>.
[4] Bray, T., Hollander, D. and A. Layman, "Namespaces in XML", W3C
REC-xml-names, January 1999, <http://www.w3.org/TR/
REC-xml-names>.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[6] Saint-Andre, P., "End-to-End Object Encryption in XMPP",
draft-ietf-xmpp-e2e-05 (work in progress), August 2003.
Informative References
[7] Jabber Software Foundation, "Jabber Software Foundation",
<http://www.jabber.org/>.
[8] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000.
[9] Dawson, F. and T. Howes, "vCard MIME Directory Profile", RFC
2426, September 1998.
Saint-Andre & Miller Expires April 25, 2004 [Page 88]
Internet-Draft XMPP Instant Messaging October 2003
Authors' Addresses
Peter Saint-Andre
Jabber Software Foundation
EMail: stpeter@jabber.org
Jeremie Miller
Jabber Software Foundation
EMail: jeremie@jabber.org
Appendix A. vCards
Sections 3.1.3 and 4.1.4 of RFC 2779 [2] 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 [9] 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 "JEP-0054:
vcard-temp", published by the Jabber Software Foundation [7]).
Appendix B. XML Schemas
The following XML schemas are descriptive, not normative. For schemas
defining the core features of XMPP, refer to XMPP Core [1].
B.1 jabber:client
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
xmlns:xml='http://www.w3.org/XML/1998/namespace'
targetNamespace='jabber:client'
xmlns='jabber:client'
elementFormDefault='qualified'>
<xs:import namespace='http://www.w3.org/XML/1998/namespace'
schemaLocation='http://www.w3.org/2001/xml.xsd'/>
<xs:element name='message'>
<xs:complexType>
<xs:sequence>
<xs:element ref='subject'
minOccurs='0'
maxOccurs='unbounded'/>
Saint-Andre & Miller Expires April 25, 2004 [Page 89]
Internet-Draft XMPP Instant Messaging October 2003
<xs:element ref='body'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='thread'
minOccurs='0'
maxOccurs='1'/>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='to'
type='xs:string'
use='optional'/>
<xs:attribute name='from'
type='xs:string'
use='optional'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute ref='xml:lang' use='optional'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='chat'/>
<xs:enumeration value='error'/>
<xs:enumeration value='groupchat'/>
<xs:enumeration value='headline'/>
<xs:enumeration value='normal'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='body' type='xs:string'>
<xs:complexType>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='subject' type='xs:string'>
<xs:complexType>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
Saint-Andre & Miller Expires April 25, 2004 [Page 90]
Internet-Draft XMPP Instant Messaging October 2003
<xs:element name='thread' type='xs:NMTOKEN'/>
<xs:element name='presence'>
<xs:complexType>
<xs:sequence>
<xs:element ref='show'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='status'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='priority'
minOccurs='0'
maxOccurs='1'/>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='to'
type='xs:string'
use='optional'/>
<xs:attribute name='from'
type='xs:string'
use='optional'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute ref='xml:lang' use='optional'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='subscribe'/>
<xs:enumeration value='subscribed'/>
<xs:enumeration value='unsubscribe'/>
<xs:enumeration value='unsubscribed'/>
<xs:enumeration value='unavailable'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='show'>
<xs:simpleType>
Saint-Andre & Miller Expires April 25, 2004 [Page 91]
Internet-Draft XMPP Instant Messaging October 2003
<xs:restriction base='xs:NCName'>
<xs:enumeration value='away'/>
<xs:enumeration value='chat'/>
<xs:enumeration value='dnd'/>
<xs:enumeration value='xa'/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name='status' type='xs:string'>
<xs:complexType>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='priority' type='xs:byte'/>
<xs:element name='iq'>
<xs:complexType>
<xs:sequence>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='error'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='to'
type='xs:string'
use='optional'/>
<xs:attribute name='from'
type='xs:string'
use='optional'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='required'/>
<xs:attribute ref='xml:lang' use='optional'/>
<xs:attribute name='type' use='required'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='get'/>
<xs:enumeration value='set'/>
<xs:enumeration value='result'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
Saint-Andre & Miller Expires April 25, 2004 [Page 92]
Internet-Draft XMPP Instant Messaging October 2003
</xs:element>
<xs:element name='error'>
<xs:complexType>
<xs:sequence>
<xs:any namespace='urn:ietf:params:xml:ns:xmpp-stanzas'
maxOccurs='1'/>
<text namespace='urn:ietf:params:xml:ns:xmpp-stanzas'
minOccurs='0'
maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='type' use='required'/>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='cancel'/>
<xs:enumeration value='continue'/>
<xs:enumeration value='modify'/>
<xs:enumeration value='auth'/>
<xs:enumeration value='wait'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
</xs:schema>
B.2 jabber:server
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
xmlns:xml='http://www.w3.org/XML/1998/namespace'
targetNamespace='jabber:server'
xmlns='jabber:server'
elementFormDefault='qualified'>
<xs:import namespace='http://www.w3.org/XML/1998/namespace'
schemaLocation='http://www.w3.org/2001/xml.xsd'/>
<xs:element name='message'>
<xs:complexType>
Saint-Andre & Miller Expires April 25, 2004 [Page 93]
Internet-Draft XMPP Instant Messaging October 2003
<xs:sequence>
<xs:element ref='subject'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='body'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='thread'
minOccurs='0'
maxOccurs='1'/>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='to'
type='xs:string'
use='required'/>
<xs:attribute name='from'
type='xs:string'
use='required'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute ref='xml:lang' use='optional'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='chat'/>
<xs:enumeration value='error'/>
<xs:enumeration value='groupchat'/>
<xs:enumeration value='headline'/>
<xs:enumeration value='normal'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='body' type='xs:string'>
<xs:complexType>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='subject' type='xs:string'>
Saint-Andre & Miller Expires April 25, 2004 [Page 94]
Internet-Draft XMPP Instant Messaging October 2003
<xs:complexType>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='thread' type='xs:NMTOKEN'/>
<xs:element name='presence'>
<xs:complexType>
<xs:sequence>
<xs:element ref='show'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='status'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='priority'
minOccurs='0'
maxOccurs='1'/>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='to'
type='xs:string'
use='required'/>
<xs:attribute name='from'
type='xs:string'
use='required'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute ref='xml:lang' use='optional'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='subscribe'/>
<xs:enumeration value='subscribed'/>
<xs:enumeration value='unsubscribe'/>
<xs:enumeration value='unsubscribed'/>
<xs:enumeration value='unavailable'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
Saint-Andre & Miller Expires April 25, 2004 [Page 95]
Internet-Draft XMPP Instant Messaging October 2003
</xs:complexType>
</xs:element>
<xs:element name='show'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='away'/>
<xs:enumeration value='chat'/>
<xs:enumeration value='dnd'/>
<xs:enumeration value='xa'/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name='status' type='xs:string'>
<xs:complexType>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='priority' type='xs:byte'/>
<xs:element name='iq'>
<xs:complexType>
<xs:sequence>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='error'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='to'
type='xs:string'
use='required'/>
<xs:attribute name='from'
type='xs:string'
use='required'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='required'/>
<xs:attribute ref='xml:lang' use='optional'/>
<xs:attribute name='type' use='required'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='get'/>
<xs:enumeration value='set'/>
<xs:enumeration value='result'/>
Saint-Andre & Miller Expires April 25, 2004 [Page 96]
Internet-Draft XMPP Instant Messaging October 2003
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='error'>
<xs:complexType>
<xs:sequence>
<xs:any namespace='urn:ietf:params:xml:ns:xmpp-stanzas'
maxOccurs='1'/>
<text namespace='urn:ietf:params:xml:ns:xmpp-stanzas'
minOccurs='0'
maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='type' use='required'/>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='cancel'/>
<xs:enumeration value='continue'/>
<xs:enumeration value='modify'/>
<xs:enumeration value='auth'/>
<xs:enumeration value='wait'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
</xs:schema>
B.3 session
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-session'
xmlns='urn:ietf:params:xml:ns:xmpp-session'
elementFormDefault='qualified'>
<xs:element name='session' type='empty'/>
Saint-Andre & Miller Expires April 25, 2004 [Page 97]
Internet-Draft XMPP Instant Messaging October 2003
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
B.4 jabber:iq:privacy
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:iq:privacy'
xmlns='jabber:iq:privacy'
elementFormDefault='qualified'>
<xs:element name='query'>
<xs:complexType>
<xs:sequence>
<xs:element ref='active'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='default'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='list'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='active'>
<xs:complexType>
<xs:attribute name='name'
type='xs:string'
use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='default'>
<xs:complexType>
<xs:attribute name='name'
type='xs:string'
use='optional'/>
</xs:complexType>
Saint-Andre & Miller Expires April 25, 2004 [Page 98]
Internet-Draft XMPP Instant Messaging October 2003
</xs:element>
<xs:element name='list'>
<xs:complexType>
<xs:sequence>
<xs:element ref='item'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:sequence>
<xs:attribute name='name'
type='xs:string'
use='required'/>
</xs:complexType>
</xs:element>
<xs:element name='item'>
<xs:complexType>
<xs:sequence>
<xs:element ref='iq'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='message'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='presence-in'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='presence-out'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='order'
type='xs:unsignedInt'
use='required'/>
<xs:attribute name='value'
type='xs:string'
use='optional'/>
<xs:attribute name='action' use='required'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='allow'/>
<xs:enumeration value='deny'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
Saint-Andre & Miller Expires April 25, 2004 [Page 99]
Internet-Draft XMPP Instant Messaging October 2003
<xs:enumeration value='group'/>
<xs:enumeration value='jid'/>
<xs:enumeration value='subscription'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='iq' type='empty'/>
<xs:element name='message' type='empty'/>
<xs:element name='presence-in' type='empty'/>
<xs:element name='presence-out' type='empty'/>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
B.5 jabber:iq:roster
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:iq:roster'
xmlns='jabber:iq:roster'
elementFormDefault='qualified'>
<xs:element name='query'>
<xs:complexType>
<xs:sequence>
<xs:element ref='item'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='item'>
<xs:complexType>
<xs:sequence>
<xs:element ref='group'
minOccurs='0'
maxOccurs='unbounded'/>
Saint-Andre & Miller Expires April 25, 2004 [Page 100]
Internet-Draft XMPP Instant Messaging October 2003
</xs:sequence>
<xs:attribute name='jid' type='xs:string' use='required'/>
<xs:attribute name='name' type='xs:string' use='optional'/>
<xs:attribute name='subscription' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCNAME'>
<xs:enumeration value='to'/>
<xs:enumeration value='from'/>
<xs:enumeration value='both'/>
<xs:enumeration value='none'/>
<xs:enumeration value='remove'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name='ask' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCNAME'>
<xs:enumeration value='subscribe'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='group' type='xs:string'/>
</xs:schema>
Appendix C. Differences Between Jabber Instant Messaging and XMPP
This section is non-normative.
XMPP has been adapted from the protocols originally developed in the
Jabber open-source community, which can be thought of as "XMPP 0.9".
Because there exists a large installed base of Jabber implementations
and deployments, it may be helpful to specify the key differences
between Jabber and XMPP in order to expedite and encourage upgrades
of those implementations and deployments to XMPP. This section
summarizes the differences that relate specifically to instant
messaging and presence applications, while the corresponding section
of XMPP Core [1] summarizes the differences that relate to all XMPP
applications.
C.1 Session Creation
The client-to-server authentication protocol developed in the Jabber
community assumes that every client is an IM client and therefore
Saint-Andre & Miller Expires April 25, 2004 [Page 101]
Internet-Draft XMPP Instant Messaging October 2003
initiates an IM session upon successful authentication and resource
binding, which are performed simultaneously (documention of this
protocol is contained in "JEP-0078: Non-SASL Authentication",
published by the Jabber Software Foundation [7]). XMPP maintains a
stricter separation between core functionality and IM functionality;
therefore, an IM session is not created until the client specifically
requests one using the protocol defined under Session Establishment
(Section 3).
C.2 Privacy Rules
The Jabber community began to define a protocol for communications
blocking (privacy rules) in late 2001, but that effort was deprecated
once the XMPP Working Group was formed. Therefore the protocol
defined under Blocking Communication (Section 10) is the only such
protocol defined for use in the Jabber community.
Appendix D. Revision History
Note to RFC Editor: please remove this entire appendix, and the
corresponding entries in the table of contents, prior to publication.
D.1 Changes from draft-ietf-xmpp-im-17
o Added missing server handling rules for <user@domain/resource>
cases.
o Further clarified privacy rules syntax by describing child
elements of <item/>.
o Clarified several points related to session establishment.
o Checked all references.
o Completed a thorough proofreading and consistency check of the
entire text.
D.2 Changes from draft-ietf-xmpp-im-16
o Added sentence to make explicit that blocking all communication
includes subscription-related presence stanzas.
o Added clause to make explicit that privacy rules must be applied
before handling of subscription-related presence stanzas and
corresponding generation of roster pushes.
o Added syntax and semantics section for the 'jabber:iq:roster'
Saint-Andre & Miller Expires April 25, 2004 [Page 102]
Internet-Draft XMPP Instant Messaging October 2003
namespace.
o Removed content about 'jabber:iq:last' namespace.
o Added several internal references from the security considerations
section to other sections of this document.
o Moved most delivery handling rules from XMPP IM to XMPP Core.
o Moved detailed stanza syntax descriptions from XMPP Core to XMPP
IM.
o Moved stanza schemas from XMPP Core to XMPP IM.
D.3 Changes from draft-ietf-xmpp-im-15
o Specified stream error to be sent to active session if there is a
conflict regarding session creation.
o Fixed several more typographical errors in the privacy rules
examples.
o Corrected an error regarding server handling of IQ stanzas sent to
bare JIDs.
o Added section on compliance requirements for instant messaging
server and client implementations.
o Added non-normative section on differences between Jabber usage
and XMPP specifications.
D.4 Changes from draft-ietf-xmpp-im-14
o Added subscription state charts.
o Fixed several typographical errors in the privacy rules examples.
o Changed datatype of 'order' attribute in privacy rules from
nonNegativeInteger to unsignedInt.
D.5 Changes from draft-ietf-xmpp-im-13
o Made one small change to privacy list syntax rules.
Saint-Andre & Miller Expires April 25, 2004 [Page 103]
Internet-Draft XMPP Instant Messaging October 2003
D.6 Changes from draft-ietf-xmpp-im-12
o Clarified meaning of the default message type as well as handling
of unknown or unsupported types.
o Made several small editorial changes.
D.7 Changes from draft-ietf-xmpp-im-11
o Further clarified subscription syntax and semantics.
o Further clarified presence responsibilities for clients and
servers.
o Added 'xml:lang' example to presence status.
o Added subsection on presence priority.
o Defined server handling of unsolicited presence stanzas of type
"subscribed".
o Specified default resource priority if not provided.
o Corrected several errors in the schemas.
o Added privacy list business rule regarding roster changes.
o Removed the 'jabber:iq:privacy:error' namespace (not necessary).
o Documented message type='normal'.
o Made numerous small editorial changes throughout.
D.8 Changes from draft-ietf-xmpp-im-10
o Clarified presence responsibilities for servers and clients.
o Clarified the routing and delivery rules for servers.
o Made the 'xml:lang' examples more complete.
o Corrected several errors in the unsubscribe workflow.
o Made small editorial changes in several sections.
Saint-Andre & Miller Expires April 25, 2004 [Page 104]
Internet-Draft XMPP Instant Messaging October 2003
D.9 Changes from draft-ietf-xmpp-im-09
o Clarified rules regarding allowable JID types in rosters.
o Further clarified the semantics and routing implications of
presence priorities.
o Removed several obsolete subsections.
D.10 Changes from draft-ietf-xmpp-im-08
o Removed authorization content (now addressed in XMPP Core).
o Added protocol for initiating an IM session, including schema and
IANA registration template.
o Corrected <*-condition/> elements to be <condition/>.
o Made small editorial changes to address RFC Editor requirements.
D.11 Changes from draft-ietf-xmpp-im-07
o Added several error cases for resource authorization and updated
relevant schema.
D.12 Changes from draft-ietf-xmpp-im-06
o Specified that IQ result stanzas are required in response to
roster pushes.
o Changed stanza error namespace names to conform to the format
defined in "The IETF XML Registry" as specified in XMPP Core.
o Removed note to RFC Editor regarding provisional namespace names.
D.13 Changes from draft-ietf-xmpp-im-05
o Removed use of ask='unsubscribe' per list discussion.
o Clarified handling of resource conflict during authorization.
o Added schemas for jabber:iq:auth, jabber:iq:auth:error, and
jabber:iq:privacy:error.
Saint-Andre & Miller Expires April 25, 2004 [Page 105]
Internet-Draft XMPP Instant Messaging October 2003
o Corrected several small protocol errors in the examples.
o Clarified semantics of message types.
D.14 Changes from draft-ietf-xmpp-im-04
o Specified sending of unavailable presence after unsubscribe and
subscription-cancellation actions.
o Further specified syntax and business rules for privacy lists.
o Brought error codes into line with definitions in
draft-ietf-xmpp-core.
o Added note to RFC Editor regarding provisional namespace names.
o Removed vCard content and DTD, instead pointing to JSF
documentation.
D.15 Changes from draft-ietf-xmpp-im-03
o Fixed order processing on privacy rules per list discussion.
o Made numerous small editorial changes.
D.16 Changes from draft-ietf-xmpp-im-02
o Added a great deal more detail to the narrative regarding
server-side privacy rules as well as the interaction between
rosters and subscriptions.
o Removed DTDs in favor of schemas (with the exception of vCard
XML).
o Removed non-normative documentation of authentication using
jabber:iq:auth and of in-band registration using
jabber:iq:register, since these are maintained by the Jabber
Software Foundation and are not part of the XMPP specification.
D.17 Changes from draft-ietf-xmpp-im-01
o Made numerous small editorial changes.
Saint-Andre & Miller Expires April 25, 2004 [Page 106]
Internet-Draft XMPP Instant Messaging October 2003
D.18 Changes from draft-ietf-xmpp-im-00
o Moved registration and authentication via jabber:iq:auth to
non-normative appendices.
o Changed initial presence stanza from MUST be empty to SHOULD be
empty.
o Specified that user or clients should not send presence stanzas of
type='probe'.
o Specified the algorithm for digest passwords.
D.19 Changes from draft-miller-xmpp-im-02
o Added information about the 'jabber:iq:last' protocol to meet the
requirement defined in section 3.2.4 of RFC 2779.
o Added information about the 'jabber:iq:privacy' protocol to meet
the requirement defined in section 2.3.5 of RFC 2779.
o Added information about the vCard XML protocol to meet the
requirement defined in sections 3.1.3 and 4.1.4 of RFC 2779.
o Changed the material describing authentication (but not resource
authorization) with 'jabber:iq:auth' to non-normative.
o Noted that the only watchers are subscribers.
o Nomenclature changes: (1) from "chunks" to "stanzas"; (2) from
"host" to "server"; (3) from "node" to "client" or "user" (as
appropriate).
Saint-Andre & Miller Expires April 25, 2004 [Page 107]
Internet-Draft XMPP Instant Messaging October 2003
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assignees.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
Saint-Andre & Miller Expires April 25, 2004 [Page 108]
Internet-Draft XMPP Instant Messaging October 2003
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Saint-Andre & Miller Expires April 25, 2004 [Page 109]
