view Side-By-Side changes

Network Working Group                                P. Saint-Andre, Ed.
Internet-Draft                                 XMPP Standards Foundation
Obsoletes: 3921 (if approved)                               June 6,                              July 12, 2008
Intended status: Standards Track
Expires: December 8, 2008 January 13, 2009


Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and
                                Presence
                     draft-saintandre-rfc3921bis-05
                     draft-saintandre-rfc3921bis-06

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   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 December 8, 2008. January 13, 2009.

Abstract

   This document describes defines extensions to core features of the Extensible
   Messaging and Presence Protocol (XMPP) that provide basic instant
   messaging (IM) and presence functionality in conformance with RFC
   2779.

   This document obsoletes RFC 3921.







Saint-Andre             Expires December 8, 2008 January 13, 2009                [Page 1]

Internet-Draft                   XMPP IM                       June                       July 2008


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5  6
     1.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  5  6
     1.2.  Requirements . . . . . . . . . . . . . . . . . . . . . . .  5  6
     1.3.  Functional Summary . . . . . . . . . . . . . . . . . . . .  6  8
     1.4.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  7  8
     1.5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . .  9
     1.6.  Discussion Venue . . . . . . . . . . . . . . . . . . . . .  7  9
   2.  Managing the Roster  . . . . . . . . . . . . . . . . . . . . .  8  9
     2.1.  Syntax and Semantics . . . . . . . . . . . . . . . . . . .  8 10
       2.1.1.  Roster Items . . . . . . . . . . . . . . . . . . . . . 10
         2.1.1.1.  Ask Attribute  . . .  8 . . . . . . . . . . . . . . . 10
         2.1.1.2.  Jid Attribute  . . . . . . . . . . . . . . . . . . 10
         2.1.1.3.  Name Attribute . . . . . . . . . . . . . . . . . . 10
         2.1.1.4.  Subscription Attribute . . . . . . . . . . . . . . 10
         2.1.1.5.  Group Element  . . . . . . . . . . . . . . . . . . 11
       2.1.2.  Roster Get . . . . . . . . . . . . . . . . . . . . . .  8 11
       2.1.3.  Roster Set . . . . . . . . . . . . . . . . . . . . . .  9 11
       2.1.4.  Roster Push  . . . . . . . . . . . . . . . . . . . . .  9 12
       2.1.5.  Roster Result  . . . . . . . . . . . . . . . . . . . . 10 13
       2.1.6.  Subscription Attribute . . . . . . . . . . . . . . . . 10 13
     2.2.  Retrieving the Roster on Login . . . . . . . . . . . . . . 11 14
     2.3.  Adding a Roster Item . . . . . . . . . . . . . . . . . . . 12 15
       2.3.1.  Request  . . . . . . . . . . . . . . . . . . . . . . . 15
       2.3.2.  Success Case . . . . . . . . . . . . . . . . . . . . . 12
       2.3.2. 16
       2.3.3.  Error Cases  . . . . . . . . . . . . . . . . . . . . . 14 17
     2.4.  Updating a Roster Item . . . . . . . . . . . . . . . . . . 17 21
       2.4.1.  Request  . . . . . . . . . . . . . . . . . . . . . . . 21
       2.4.2.  Success Case . . . . . . . . . . . . . . . . . . . . . 17
       2.4.2. 23
       2.4.3.  Error Cases  . . . . . . . . . . . . . . . . . . . . . 19 23
     2.5.  Deleting a Roster Item . . . . . . . . . . . . . . . . . . 19 23
       2.5.1.  Request  . . . . . . . . . . . . . . . . . . . . . . . 23
       2.5.2.  Success Case . . . . . . . . . . . . . . . . . . . . . 19
       2.5.2. 23
       2.5.3.  Error Cases  . . . . . . . . . . . . . . . . . . . . . 20 24
   3.  Managing Presence Subscriptions  . . . . . . . . . . . . . . . 20 24
     3.1.  Requesting a Subscription  . . . . . . . . . . . . . . . . 21 25
       3.1.1.  Client Generation of Outbound Subscription Request . . 21 25
       3.1.2.  Server Processing of Outbound Subscription Request . . 22 26
       3.1.3.  Server Processing of Inbound Subscription Request  . . 23 27
       3.1.4.  Client Processing of Inbound Subscription Request  . . 24 29
       3.1.5.  Server Processing of Outbound Subscription Approval  . 25 29
       3.1.6.  Server Processing of Inbound Subscription Approval . . 26 30
     3.2.  Cancelling a Subscription  . . . . . . . . . . . . . . . . 27 32
       3.2.1.  Client Generation of Subscription Cancellation . . . . 27 32
       3.2.2.  Server Processing of Outbound Subscription
               Cancellation . . . . . . . . . . . . . . . . . . . . . 27 32
       3.2.3.  Server Processing of Inbound Subscription



Saint-Andre             Expires January 13, 2009                [Page 2]

Internet-Draft                   XMPP IM                       July 2008


               Cancellation . . . . . . . . . . . . . . . . . . . . . 28 33
     3.3.  Unsubscribing  . . . . . . . . . . . . . . . . . . . . . . 29 34
       3.3.1.  Client Generation of Unsubscribe . . . . . . . . . . . 29 34
       3.3.2.  Server Processing of Outbound Unsubscribe  . . . . . . 29 34
       3.3.3.  Server Processing of Inbound Unsubscribe . . . . . . . 30 35
   4.  Exchanging Presence Information  . . . . . . . . . . . . . . . 31 36
     4.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . 31 36
     4.2.  Initial Presence . . . . . . . . . . . . . . . . . . . . . 31 37
       4.2.1.  Client Generation of Initial Presence  . . . . . . . . 31



Saint-Andre             Expires December 8, 2008                [Page 2]

Internet-Draft                   XMPP IM                       June 2008 37
       4.2.2.  Server Processing of Outbound Presence . . . . . . . . 32 38
       4.2.3.  Server Processing of Inbound Presence  . . . . . . . . 33 38
       4.2.4.  Client Processing of Inbound Presence  . . . . . . . . 33 39
     4.3.  Presence Probes  . . . . . . . . . . . . . . . . . . . . . 33 39
       4.3.1.  Server Generation of Outbound Presence Probe . . . . . 34 39
       4.3.2.  Server Processing of Inbound Presence Probe  . . . . . 34 40
     4.4.  Subsequent Presence Broadcast  . . . . . . . . . . . . . . 35 41
       4.4.1.  Client Generation of Presence Broadcast  . . . . . . . 35 41
       4.4.2.  Server Processing of Outbound Presence . . . . . . . . 36 41
       4.4.3.  Server Processing of Inbound Presence  . . . . . . . . 37 43
       4.4.4.  Client Processing of Inbound Presence  . . . . . . . . 37 43
     4.5.  Unavailable Presence . . . . . . . . . . . . . . . . . . . 37 43
       4.5.1.  Client Generation of Unavailable Presence  . . . . . . 37 43
       4.5.2.  Server Processing of Outbound Unavailable Presence . . 38 44
       4.5.3.  Server Processing of Inbound Unavailable Presence  . . 39 45
       4.5.4.  Client Processing of Inbound Unavailable Presence  . . 39 46
     4.6.  Directed Presence  . . . . . . . . . . . . . . . . . . . . 40 46
       4.6.1.  Client Generation of Directed Presence . . . . . . . . 40 46
       4.6.2.  Server Processing of Outbound Directed Presence  . . . 40 47
       4.6.3.  Server Processing of Inbound Directed Presence . . . . 41 47
       4.6.4.  Client Processing of Inbound Directed Presence . . . . 41 47
     4.7.  Presence Syntax  . . . . . . . . . . . . . . . . . . . . . 41 48
       4.7.1.  Type Attribute . . . . . . . . . . . . . . . . . . . . 41 48
       4.7.2.  Child Elements . . . . . . . . . . . . . . . . . . . . 42 49
       4.7.3.  Show Element . . . . . . . . . . . . . . . . . . . . . 42 49
       4.7.4.  Status Element . . . . . . . . . . . . . . . . . . . . 43 50
       4.7.5.  Priority Element . . . . . . . . . . . . . . . . . . . 44 51
       4.7.6.  Extended Content . . . . . . . . . . . . . . . . . . . 44 51
   5.  Exchanging Messages  . . . . . . . . . . . . . . . . . . . . . 45 52
     5.1.  Attributes . . . . . .  One-to-One Chat Sessions . . . . . . . . . . . . . . . . . 52
     5.2.  Message Syntax . 45
       5.1.1.  To Attribute . . . . . . . . . . . . . . . . . . . . . 45
       5.1.2.  Type 53
       5.2.1.  To Attribute . . . . . . . . . . . . . . . . . . . . 46
     5.2.  Child Elements . . 53
       5.2.2.  Type Attribute . . . . . . . . . . . . . . . . . . . . 47
       5.2.1. 53
       5.2.3.  Body Element . . . . . . . . . . . . . . . . . . . . . . . . . 47
       5.2.2. 55
       5.2.4.  Subject Element  . . . . . . . . . . . . . . . . . . . . . . . 48
       5.2.3. 55
       5.2.5.  Thread Element . . . . . . . . . . . . . . . . . . . . . . . . 49 56
     5.3.  Extended Content . . . . . . . . . . . . . . . . . . . . . 50
     5.4.  One-to-One Chat Sessions . . . . . . . . . . . . . . . . . 51 57
   6.  Exchanging IQ Stanzas  . . . . . . . . . . . . . . . . . . . . 51 58
   7.  A Sample Session . . . . . . . . . . . . . . . . . . . . . . . 52 58



Saint-Andre             Expires January 13, 2009                [Page 3]

Internet-Draft                   XMPP IM                       July 2008


   8.  Server Rules for Processing XML Stanzas  . . . . . . . . . . . 59 66
     8.1.  No Such User . . . . . . . . . . . . . . . . . . . . . . . 59 66
     8.2.  Full JID at Local Domain . . . . . . . . . . . . . . . . . 59 66
       8.2.1.  Available Resource Matches . . . . . . . . . . . . . . 59 66
       8.2.2.  No Available Resource Matches  . . . . . . . . . . . . 60 67
     8.3.  Bare JID at Local Domain . . . . . . . . . . . . . . . . . 60 67
       8.3.1.  Available Resources  . . . . . . . . . . . . . . . . . 60 67
         8.3.1.1.  Message  . . . . . . . . . . . . . . . . . . . . . 60



Saint-Andre             Expires December 8, 2008                [Page 3]

Internet-Draft                   XMPP IM                       June 2008 67
         8.3.1.2.  Presence . . . . . . . . . . . . . . . . . . . . . 61 68
         8.3.1.3.  IQ . . . . . . . . . . . . . . . . . . . . . . . . 61 68
       8.3.2.  No Available Resources . . . . . . . . . . . . . . . . 61 69
         8.3.2.1.  Message  . . . . . . . . . . . . . . . . . . . . . 62 69
         8.3.2.2.  Presence . . . . . . . . . . . . . . . . . . . . . 62 69
         8.3.2.3.  IQ . . . . . . . . . . . . . . . . . . . . . . . . 62 69
     8.4.  Foreign  Remote Domain  . . . . . . . . . . . . . . . . . . . . . . 63 70
   9.  IM and Presence Compliance Requirements  . . . . . . . . . . . 64 71
     9.1.  Servers  . . . . . . . . . . . . . . . . . . . . . . . . . 64 71
     9.2.  Clients  . . . . . . . . . . . . . . . . . . . . . . . . . 64 71
   10. Internationalization Considerations  . . . . . . . . . . . . . 65 72
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 65 72
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 66 73
     12.1. Instant Messaging SRV Protocol Label Registration  . . . . 66 73
     12.2. Presence SRV Protocol Label Registration . . . . . . . . . 66 73
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 67 74
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 67 74
     13.2. Informative References . . . . . . . . . . . . . . . . . . 68 75
   Appendix A.  Subscription States . . . . . . . . . . . . . . . . . 69 76
     A.1.  Defined States . . . . . . . . . . . . . . . . . . . . . . 69 76
     A.2.  Server Processing of Outbound Presence Subscription
           Stanzas  . . . . . . . . . . . . . . . . . . . . . . . . . 70 77
       A.2.1.  Subscribe  . . . . . . . . . . . . . . . . . . . . . . 71 78
       A.2.2.  Unsubscribe  . . . . . . . . . . . . . . . . . . . . . 71 78
       A.2.3.  Subscribed . . . . . . . . . . . . . . . . . . . . . . 72 79
       A.2.4.  Unsubscribed . . . . . . . . . . . . . . . . . . . . . 72 79
     A.3.  Server Processing of Inbound Presence Subscription
           Stanzas  . . . . . . . . . . . . . . . . . . . . . . . . . 73 80
       A.3.1.  Subscribe  . . . . . . . . . . . . . . . . . . . . . . 73 80
       A.3.2.  Unsubscribe  . . . . . . . . . . . . . . . . . . . . . 73 80
       A.3.3.  Subscribed . . . . . . . . . . . . . . . . . . . . . . 74 81
       A.3.4.  Unsubscribed . . . . . . . . . . . . . . . . . . . . . 75 82
   Appendix B.  Blocking Communication  . . . . . . . . . . . . . . . 76 83
   Appendix C.  vCards  . . . . . . . . . . . . . . . . . . . . . . . 76 83
   Appendix D.  XML Schemas . . . . . . . . . . . . . . . . . . . . . 76 83
     D.1.  jabber:client  . . . . . . . . . . . . . . . . . . . . . . 76 83
     D.2.  jabber:server  . . . . . . . . . . . . . . . . . . . . . . 80 88
     D.3.  jabber:iq:roster . . . . . . . . . . . . . . . . . . . . . 85 92
   Appendix E.  Differences From RFC 3921 . . . . . . . . . . . . . . 86 93
   Appendix F.  Copying Conditions  . . . . . . . . . . . . . . . . . 86 94



Saint-Andre             Expires January 13, 2009                [Page 4]

Internet-Draft                   XMPP IM                       July 2008


   Index  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 94
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 87 95
   Intellectual Property and Copyright Statements . . . . . . . . . . 89 96
















































Saint-Andre             Expires December 8, 2008 January 13, 2009                [Page 4] 5]

Internet-Draft                   XMPP IM                       June                       July 2008


1.  Introduction

1.1.  Overview

   The Extensible Messaging and Presence Protocol (XMPP) is an
   application profile of the Extensible Markup Language [XML] for
   streaming XML data in close to real time between any two (or more)
   network-aware entities.  XMPP is typically used to exchange messages,
   share presence information, and engage in structured request-response
   interactions.  The core features of XMPP defined in [XMPP-CORE]
   provide the building blocks for many types of near-real-time
   applications, which may can be layered on top of the core by sending
   application-specific data qualified by particular XML namespaces
   (refer to [XML-NAMES]).  This document describes defines XMPP extensions that
   provide the basic functionality expected of an instant messaging (IM)
   and presence application as defined in [IMP-REQS].

   This

   As a result of extensive implementation and deployment experience
   with XMPP since 2004, as well as more formal interoperability testing
   carried out under the auspices of the XMPP Standards Foundation
   (XSF), this document obsoletes reflects consensus from the XMPP developer
   community regarding XMPP's basic instant messaging and presence
   features.  In particular, this document incorporates the following
   backward-compatible changes from RFC 3921:

   o  Incorporated corrections and errata
   o  Added examples throughout
   o  Clarified and more completely specified matters that were
      underspecified
   o  Removed the protocol for session establishment, which was deemed
      unnecessary
   o  Modified error handling related to presence stanzas to more
      seamlessly repair lack of synchronization in subscription states
      between rosters located at different servers
   o  Added optional server support for pre-approved presence
      subscriptions
   o  Added optional 'parent' attribute to <thread/> element
   o  Transferred documentation for the communications blocking protocol
      from this specification to a separate specification

   Therefore, this document defines the basic instant messaging and
   presence features of XMPP 1.0, thus obsoleting RFC 3921.

1.2.  Requirements

   Traditionally, instant messaging applications have combined the
   following factors:




Saint-Andre             Expires January 13, 2009                [Page 6]

Internet-Draft                   XMPP IM                       July 2008


   1.  The central point of focus is a list of one's contacts or
       "buddies" (in XMPP this list is called a ROSTER).
   2.  The purpose of using such an application is to exchange
       relatively brief text messages with each of one's particular contacts in close
       to real time -- often relatively large numbers of such messages
       in rapid succession, in the form of a one-to-one chat
       sessions CHAT SESSION as
       described under Section 5.4. 5.1.
   3.  The catalyst for exchanging messages is PRESENCE -- i.e.,
       information about the network availability of each of one's particular contacts
       (thus knowing who is online and available for a one-to-
       one one-to-one chat
       session).
   4.  Presence information is provided only to contacts that a user one has
       authorized via by means of an explicit agreement called a presence subscription. PRESENCE
       SUBSCRIPTION.

   Thus at a high level this document assumes that a user must be able
   to complete the following use cases:

   o  Manage items in one's contact list
   o  Exchange messages with one's contacts
   o  Exchange presence information with one's contacts
   o  Manage presence subscriptions to and from one's contacts

   Detailed definitions of these functionality areas are contained in
   RFC 2779 [IMP-REQS], and the interested reader is referred to that



Saint-Andre             Expires December 8, 2008                [Page 5]

Internet-Draft                   XMPP IM                       June 2008
   document regarding the requirements addressed herein.  While the XMPP
   instant messaging and presence extensions specified herein meet the
   requirements of RFC 2779, they were not designed explicitly with that
   specification in mind, since the base protocol evolved through an
   open development process within the Jabber open-source community
   before RFC 2779 was written.  Although XMPP protocol extensions
   addressing many other functionality areas have been defined in the
   XMPP Standards Foundation's XEP series (e.g., multi-user text chat as
   specified in [XEP-0045]), such extensions are not specified in this
   document because they are not required mandated by RFC 2779.

   Note: RFC 2779 stipulates that presence services must be separable
   from instant messaging services and vice-versa; i.e., it must be
   possible to use the protocol to provide a presence service, an
   instant messaging service, or both.  Although the text of this
   document assumes that implementations and deployments will want to
   offer a unified instant messaging and presence service, there is no
   requirement that a service must offer both a presence service and an
   instant messaging service, and the protocol makes it possible to
   offer separate and distinct services for presence and for instant
   messaging.  (For example, a presence-only service could return a
   <service-unavailable/> stanza error if a client attempt to send a
   <message/>
   stanzas.) stanza.)



Saint-Andre             Expires January 13, 2009                [Page 7]

Internet-Draft                   XMPP IM                       July 2008


1.3.  Functional Summary

   This non-normative section provides a developer-friendly, functional
   summary of XMPP-based instant messaging and presence features; refer
   to
   consult the sections that follow for a normative definition of these
   features.

   [XMPP-CORE] specifies how an XMPP client connects to an XMPP server.
   In particular, it specifies the preconditions that must be fulfilled
   before a client is allowed to send XML stanzas (the basic unit of
   meaning in XMPP) to other entities on an XMPP network.  These
   preconditions comprise negotiation of the XML stream and include XML
   stream establishment, optional channel encryption via Transport Layer
   Security [TLS], mandatory authentication via Simple Authentication
   and Security Layer [SASL], and binding of a resource to the stream
   for client addressing.  The reader is referred to [XMPP-CORE] for
   details regarding these preconditions, and knowledge of [XMPP-CORE]
   is assumed herein.

   Upon fulfillment of the preconditions specified in [XMPP-CORE], an
   XMPP client has a long-lived XML stream with an XMPP server, which
   enables the user controlling that client to send and receive a
   potentially unlimited number of XML stanzas over the stream.  Such a
   stream can be used to exchange messages, share presence information,
   and engage in



Saint-Andre             Expires December 8, 2008                [Page 6]

Internet-Draft                   XMPP IM                       June 2008 structured request-response interactions in close to
   real time.  After negotiation of the XML stream, the typical flow for
   an instant messaging and presence session is as follows:

   1.  Retrieve one's roster.  (See Section 2.2.)
   2.  Send initial presence to the server for broadcasting to all
       subscribed contacts, thus "going online" from the perspective of
       XMPP communications. communication.  (See Section 4.2.)
   3.  Exchange messages, manage presence subscriptions, perform roster
       updates, and in general process and generate other XML stanzas
       with particular semantics throughout the life of the session.
       (See Section 5, Section 3, Section 2, and Section 6.)
   4.  Terminate the session when desired by sending unavailable
       presence and closing the underlying XML stream.  (See
       Section 4.5.)

1.4.  Conventions

   This document inherits the terminology defined in [XMPP-CORE].

   The following keywords are to be interpreted as described in [TERMS]:
   "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD",
   "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".




Saint-Andre             Expires January 13, 2009                [Page 8]

Internet-Draft                   XMPP IM                       July 2008


   For convenience, this document employs the term "user" to refer to
   the owner of an XMPP account; however, account owners need not be
   human persons and may can be bots, devices, or other non-human
   applications.

   In examples, lines have been wrapped

   Following the "XML Notation" used in [IRI] to represent characters
   that cannot be rendered in ASCII-only documents, some examples in
   this document use the form "&#x...." as a notational device to
   represent Unicode characters (e.g., the string "&#x0159;" stands for
   the Unicode character LATIN SMALL LETTER R WITH CARON).

   In examples, lines have been wrapped for improved readability,
   "[...]" means elision, and the following prepended strings are used: used
   (these prepended strings are not to be sent over the wire):

   o  C: = client
   o  CC: = contact's client
   o  CS: = contact's server
   o  S: = server
   o  UC: = user's client
   o  US: = user's server

1.5.  Acknowledgements

   The editor of this document finds it impossible to appropriately
   acknowledge the many individuals who have provided comments regarding
   the protocols defined herein.  However, thanks are due to those who
   have who have provided implementation feedback, bug reports, requests
   for clarification, and suggestions for improvement since the
   publication of the RFC this document supersedes.  The editor has
   endeavored to address all such feedback, but is solely responsible
   for any remaining errors and ambiguities.

1.6.  Discussion Venue

   The document editor welcomes and the broader XMPP developer community welcome
   discussion and comments related to the topics presented in this
   document.  The preferred forum is the <standards@xmpp.org> mailing
   list, for which archives and subscription information are available
   at
   <<http://mail.jabber.org/mailman/listinfo/standards>>.





Saint-Andre             Expires December 8, 2008                [Page 7]

Internet-Draft                   XMPP IM                       June 2008 <http://mail.jabber.org/mailman/listinfo/standards>.


2.  Managing the Roster

   In XMPP, one's roster contains any number of specific contacts.  A
   user's roster is stored by the user's server on the user's behalf so
   that the user may can access roster information from any resource.




Saint-Andre             Expires January 13, 2009                [Page 9]

Internet-Draft                   XMPP IM                       July 2008


2.1.  Syntax and Semantics

   Rosters are managed using IQ stanzas, specifically by means of a
   <query/> child element qualified by the 'jabber:iq:roster' namespace.
   The detailed syntax and semantics are defined in the following
   sections.

2.1.1.  Roster Items

   The <query/> element MAY contain one or more <item/> children, each
   describing a unique roster item ROSTER ITEM or "contact".

   The syntax of the <item/> element is as follows:

   1. described in the following
   sections.

2.1.1.1.  Ask Attribute

   The 'jid' 'ask' attribute is REQUIRED; the value used to specify certain subscription sub-
   states; for details, see Section 3.1.2.

   Inclusion of this the 'ask' attribute is OPTIONAL.

2.1.1.2.  Jid Attribute

   The 'jid' attribute specifies the Jabber Identifier (JID) that
   uniquely identifies the roster item.
   2.  The 'name'

   Inclusion of the 'jid' attribute is OPTIONAL; the value of this REQUIRED.

2.1.1.3.  Name Attribute

   The 'name' attribute specifies the "handle" to be associated with the
   JID, as determined by the user (not the contact).  While  Although the value
   of the 'name' attribute may MAY have meaning to a human user, typically it is
   opaque to the server (although it server.  However, the 'name' attribute MAY be used by
   the server for matching purposes within the context of various XMPP
       extensions).
   3.
   extensions, in which case the values MUST be compared only after
   application of the Resourceprep profile of stringprep as defined in
   [XMPP-CORE].

   Inclusion of the 'name' attribute is OPTIONAL.

2.1.1.4.  Subscription Attribute

   The 'subscription' attribute is OPTIONAL; see Section 2.1.6.
   4.  The 'ask'

   Inclusion of the 'subscription' attribute is OPTIONAL and is used to specify certain
       subscription sub-states; for details, see Section 3.1.2.
   5.  The <group/> element is OPTIONAL; the XML character data of this OPTIONAL.




Saint-Andre             Expires January 13, 2009               [Page 10]

Internet-Draft                   XMPP IM                       July 2008


2.1.1.5.  Group Element

   The <group/> child element specifies a category or "bucket" into
   which the roster item should is to be grouped by a client.  The  An <item/>
   element MAY contain more than one <group/> element.  The element, so that roster
   groups are not exclusive.  Although the XML character data of the
   <group/> element
       is typically opaque to the server but may MAY have meaning to a human
       user. user, it is opaque to
   the server.  However, the <group/> element MAY be used by the server
   for matching purposes within the context of various XMPP extensions,
   in which case the data MUST be compared only after application of the
   Resourceprep profile of stringprep as defined in [XMPP-CORE].

   Inclusion of the <group/> child element is OPTIONAL.

2.1.2.  Roster Get

   A ROSTER GET is a client's request for the server to send the roster;
   syntactically it is an IQ stanza of type "get" sent from client to
   server and containing a <query/> element qualified by the 'jabber:iq:roster'
   namespace.

   The 'jabber:iq:
   roster' namespace, where the <query/> element in a roster get MUST NOT contain any
   <item/> child elements.




Saint-Andre             Expires December 8, 2008                [Page 8]

Internet-Draft                   XMPP IM                       June 2008

   C: <iq from='juliet@example.com/balcony'
          type='get'
          id='roster_get'>
          id='rg1'
          type='get'>
       <query xmlns='jabber:iq:roster'/>
     </iq>

   The expected outcome of sending a roster get is for the server to
   return a roster result.

2.1.3.  Roster Set

   A ROSTER SET is a client's request for the server to modify (i.e.,
   create, update, or delete) a roster item; syntactically it is an IQ
   stanza of type "set" sent from client to server and containing a
   <query/> element qualified by the 'jabber:iq:roster' namespace.

   The following rules apply to roster sets:

   1.  The <query/> element MUST contain one and only one <item/>
       element.
   2.  A receiving  The server MUST ignore any value of the 'subscription' attribute
       other than "remove" (see Section 2.1.6).
   3.  A receiving  The server MUST ignore any 'to' address specified on the IQ
       stanza and MUST handle the IQ stanza as if it included no 'to'
       attribute.




Saint-Andre             Expires January 13, 2009               [Page 11]

Internet-Draft                   XMPP IM                       July 2008


   C: <iq from='juliet@example.com/balcony'
          type='set'
          id='roster_set'>
          id='rs1'
          type='set'>
       <query xmlns='jabber:iq:roster'>
         <item jid='nurse@example.com'/>
       </query>
     </iq>

2.1.4.  Roster Push

   A ROSTER PUSH is a newly created, updated, or deleted roster item
   that is sent from the server to the client; syntactically it is an IQ
   stanza of type "set" sent from server to client and containing a
   <query/> element qualified by the 'jabber:iq:
   roster' 'jabber:iq:roster' namespace.

   The following rules apply to roster pushes:

   1.  The <query/> element in a roster push MUST contain one and only
       one <item/> element.
   2.  A receiving client MUST ignore the stanza unless it has no 'from'
       attribute (i.e., implicitly from the server) user's bare JID) or it has a
       'from' attribute whose value matches the user's bare JID
       <user@domain>.








Saint-Andre             Expires December 8, 2008                [Page 9]

Internet-Draft                   XMPP IM                       June 2008

   S: <iq id='a78b4q6ha463'
          to='juliet@example.com/chamber'
          type='set'
          id='roster_push'>
          type='set'>
       <query xmlns='jabber:iq:roster'>
         <item jid='nurse@example.com'/>
       </query>
     </iq>

2.1.5.  Roster Result

   A ROSTER RESULT is

   As mandated by the semantics of the IQ stanza as defined in
   [XMPP-CORE], each resource that receives a roster push MUST reply
   with an IQ stanza of type "result" sent from server to
   client and containing a <query/> element qualified by the 'jabber:iq:
   roster' namespace. (or "error").

   C: <iq from='juliet@example.com/balcony'
          id='a78b4q6ha463'
          type='result'/>

   C: <iq from='juliet@example.com/chamber'
          id='a78b4q6ha463'
          type='result'/>

      Note: There is no error case for client processing of roster
      pushes; if the server receives an IQ of type "error" in response
      to a roster push it SHOULD ignore the error.




Saint-Andre             Expires January 13, 2009               [Page 12]

Internet-Draft                   XMPP IM                       July 2008


2.1.5.  Roster Result

   A ROSTER RESULT is the server's response to a roster get;
   syntactically it is an IQ stanza of type "result" sent from server to
   client and containing a <query/> element qualified by the 'jabber:iq:
   roster' namespace.

   The <query/> element in a roster result contains one <item/> element
   for each contact and therefore MAY can contain more than one <item/>
   element.

   S: <iq id='rg1'
          to='juliet@example.com/chamber'
          type='result'
          id='roster_result'>
          type='result'>
       <query xmlns='jabber:iq:roster'>
         <item jid='nurse@example.com'/>
         <item jid='romeo@example.net'/>
       </query>
     </iq>

   If there are no contacts in the roster, the <query/> element MUST be
   empty.

   S: <iq to='juliet@example.com/chamber'
          type='result'
          id='roster_result'>
          id='roster_result'
          type='result'>
       <query xmlns='jabber:iq:roster'/>
     </iq>

2.1.6.  Subscription Attribute

   The state of the presence subscription in relation to a roster item
   is captured in the 'subscription' attribute of the <item/> element.
   Allowable subscription-related values for this attribute are:

   o  "none" -- the user does not have a subscription to the contact's
      presence, and the contact does not have a subscription to the
      user's presence
   o  "to" -- the user has a subscription to the contact's presence, but
      the contact does not have a subscription to the user's presence




Saint-Andre             Expires December 8, 2008               [Page 10]

Internet-Draft                   XMPP IM                       June 2008
   o  "from" -- the contact has a subscription to the user's presence,
      but the user does not have a subscription to the contact's
      presence
   o  "both" -- both the user and the contact have subscriptions to each
      other's presence (also called a "mutual subscription")

   In a roster result, a receiving the client MUST ignore values of the
   'subscription' attribute other than "none", "to", "from", or "both".



Saint-Andre             Expires January 13, 2009               [Page 13]

Internet-Draft                   XMPP IM                       July 2008


   In a roster push, a receiving the client MUST ignore values of the 'subscription'
   attribute other than "none", "to", "from", "both", or "remove".

   In a roster set, the value of the 'subscription' attribute MAY be
   included with a value of "remove", which indicates that the item is
   to be removed from the roster; a receiving the server MUST ignore all values of
   the 'subscription' attribute other than "remove".

2.2.  Retrieving the Roster on Login

   Upon authenticating with a server and binding a resource (thus
   becoming a connected resource), a client SHOULD request the roster
   before sending initial presence (however, because receiving the
   roster may is not be necessarily desirable for all resources, e.g., a
   connection with limited bandwidth, the client's request for the
   roster is
   recommended and not required). mandatory).  After a connected resource sends initial
   presence (see Section 4.2), it is referred to as an available
   resource.  If a connected resource or available resource requests the roster but does not
   send initial presence, the
   roster, it is referred to as an INTERESTED RESOURCE.  The server MUST NOT
   send it presence roster pushes to all interested resources.

      Note: Presence subscription requests and SHOULD NOT send it associated roster
   pushes.  If an are sent to available resource does not request
      resources, whereas the roster during
   a session, the server SHOULD NOT send it presence subscription
   requests and MUST NOT send it pushes associated roster pushes.  Therefore, with subscription
      state changes are sent to interested resources.  Therefore if a client
      resource wishes to engage in the full range of interactions
   related to contact lists (rosters) receive both subscription requests and presence subscriptions, roster
      pushes, it
   SHOULD MUST both request the roster and send initial presence.  For the
   sake of brevity, the term INTERESTED RESOURCE is used herein to refer
   to the concept of "an available resource that has requested presence and request the
   roster". roster.

   A client requests the roster by sending a roster get over its stream
   to the server.

   C: <iq from='juliet@example.com/balcony' type='get' id='roster_1'>
          id='roster_1'
          type='get'>
        <query xmlns='jabber:iq:roster'/>
      </iq>
















Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 11] 14]

Internet-Draft                   XMPP IM                       June                       July 2008


   S: <iq id='roster_1'
          to='juliet@example.com/balcony' type='result' id='roster_1'>
          type='result'>
        <query xmlns='jabber:iq:roster'>
          <item jid='romeo@example.net'
                name='Romeo'
                subscription='both'>
            <group>Friends</group>
          </item>
          <item jid='mercutio@example.org' jid='mercutio@example.com'
                name='Mercutio'
                subscription='from'/>
          <item jid='nurse@example.com'
               name='Nurse'
               subscription='to'/>
         <item jid='benvolio@example.org' jid='benvolio@example.net'
                name='Benvolio'
                subscription='both'/>
        </query>
      </iq>

   If the server cannot process the roster get, it MUST return an
   appropriate stanza error as described in [XMPP-CORE] (such as
   <service-unavailable/> if the roster namespace is not supported or
   <internal-server-error/> if the server experiences trouble processing
   or returning the roster).

2.3.  Adding a Roster Item

2.3.1.  Success Case  Request

   At any time, a client may can add an item to the roster roster.  This is done by
   sending a roster set to the server.

   Note: When the item added represents another IM user, the value of
   the 'jid' attribute MUST be a bare JID <contact@domain> rather containing a full
   JID <contact@domain/resource>, since the desired result is for the
   user to receive presence from all of the contact's resources, not
   merely the particular resource specified in the 'to' attribute. new item.

   C: <iq from='juliet@example.com/balcony' type='set' id='roster_2'>
          id='roster_2'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='Nurse'>
            <group>Servants</group>
          </item>
        </query>
      </iq>

      Note: When a user adds a contact for the purpose of tracking the
      user's presence subscription to a contact, the user's client MUST
      send a presence subscription request to the contact before
      generating any roster set related to the contact.  This enables
      the user's server to enforce any policies relevant to presence
      subscriptions (e.g., a prohibition on presence subscriptions to



Saint-Andre             Expires January 13, 2009               [Page 15]

Internet-Draft                   XMPP IM                       July 2008


      full JIDs).  For details, see Section 3.

2.3.2.  Success Case

   If the server can successfully process the roster set (i.e., if none



Saint-Andre             Expires December 8, 2008               [Page 12]

Internet-Draft                   XMPP IM                       June 2008
   of the error cases occurs), it MUST create the roster item in
   persistent storage and storage.

   The server MUST then return an IQ stanza of type "result" to the
   connected resource that sent the roster set.

   S: <iq id='roster_2'
          to='juliet@example.com/balcony'
          type='result'/>

   The server MUST also send a roster push containing the new roster
   item to all of the user's interested resources. resources, including the
   resource that generated the roster set.

   S: <iq to='juliet@example.com/balcony'
          type='set'
          id='a78b4q6ha463'>
          id='a78b4q6ha463'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='Nurse'
                subscription='none'>
            <group>Servants</group>
          </item>
        </query>
      </iq>

   S: <iq to='juliet@example.com/chamber'
          type='set'
          id='a78b4q6ha464'>
          id='a78b4q6ha464'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='Nurse'
                subscription='none'>
            <group>Servants</group>
          </item>
        </query>
      </iq>

   The server MUST also return an IQ stanza of type "result" to the
   connected resource that sent the roster set.

   S: <iq to='juliet@example.com/balcony' type='result' id='roster_2'/>

   As required mandated by the semantics of the IQ stanza as defined in
   [XMPP-CORE], each resource that received the receives a roster push MUST reply
   with an IQ stanza of type "result" (or "error").





Saint-Andre             Expires January 13, 2009               [Page 16]

Internet-Draft                   XMPP IM                       July 2008


   C: <iq from='juliet@example.com/balcony'
         type='result'
         id='a78b4q6ha463'/>
          id='a78b4q6ha463'
          type='result'/>

   C: <iq from='juliet@example.com/chamber'
         type='result'
         id='a78b4q6ha464'/>

   Note: There is no error case for client replies to roster pushes, and
   if the server receives an IQ of type "error" in response to a roster
   push it SHOULD ignore the error.




Saint-Andre             Expires December 8, 2008               [Page 13]

Internet-Draft                   XMPP IM                       June 2008


2.3.2.
          id='a78b4q6ha464'
          type='result'/>

2.3.3.  Error Cases

   If the server cannot successfully process the roster set, it MUST
   return an a stanza error.  The following error cases are defined
   (naturally, other stanza errors may can occur, e.g., <internal-server-error/>). such as <internal-server-
   error/>).

   The server SHOULD return a <bad-request/> stanza error to the client
   if the roster set violates any of the following conditions:

   1.  The <query/> element contains more than one <item/> child
       element.
   2.  The <item/> element contains more than one <group/> element, but
       there are duplicate groups (where duplicates are determined using
       the Resourceprep profile of stringprep as defined in
       [XMPP-CORE]).

   The server SHOULD return a <not-acceptable/> stanza error to the
   client if the roster set violates any of the following conditions:

   1.  The value of the 'name' attribute is greater than a server-
       configured limit.
   2.  The XML character data of the <group/> element is of zero length.
   3.  The XML character data of the <group/> element is greater than a
       server-configured limit.

   Alternatively, the server MAY ignore the foregoing violations and
   process the roster set as best as possible (e.g., process only the
   first <item/> element, ignore duplicate <group/> elements, place the
   roster item in no group or a default group if the <group/> element is
   empty, and truncate 'name' attributes and <group/> elements that are
   too long).











Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 14] 17]

Internet-Draft                   XMPP IM                       June                       July 2008


   Error: Roster set contains more than one item

   C: <iq from='juliet@example.com/balcony' type='set' id='roster_3'>
          id='roster_3'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='Nurse'>
            <group>Servants</group>
          </item>
          <item jid='mother@example.com'
                name='Mom'>
            <group>Family</group>
          </item>
        </query>
      </iq>

   S: <iq id='roster_3'
          to='juliet@example.com/balcony' type='error' id='roster_3'>
          type='error'>
       <error type='modify'>
         <bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
       </error>
     </iq>

   Error: Roster set contains item with oversized handle

   C: <iq from='juliet@example.com/balcony' type='set' id='roster_4'>
          id='roster_4'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='[ ... some-very-long-handle ... ]'>
            <group>Servants</group>
          </item>
        </query>
      </iq>

   S: <iq id='roster_4'
          to='juliet@example.com/balcony' type='error' id='roster_4'>
          type='error'>
        <error type='modify'>
          <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
        </error>
      </iq>






Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 15] 18]

Internet-Draft                   XMPP IM                       June                       July 2008


   Error: Roster set contains duplicate groups

   C: <iq from='juliet@example.com/balcony' type='set' id='roster_5'>
          id='roster_5'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='Nurse'>
            <group>Servants</group>
            <group>Servants</group>
          </item>
        </query>
      </iq>

   S: <iq id='roster_5'
          to='juliet@example.com/balcony' type='error' id='roster_5'>
          type='error'>
        <error type='modify'>
          <bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
        </error>
      </iq>

   Error: Roster set contains empty group

   C: <iq from='juliet@example.com/balcony' type='set' id='roster_6'>
          id='roster_6'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='Nurse'>
            <group></group>
          </item>
        </query>
      </iq>

   S: <iq id='roster_6'
          to='juliet@example.com/balcony' type='error' id='roster_6'>
          type='error'>
        <error type='modify'>
          <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
        </error>
      </iq>









Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 16] 19]

Internet-Draft                   XMPP IM                       June                       July 2008


   Error: Roster set contains oversized group

   C: <iq from='juliet@example.com/balcony' type='set' id='roster_7'>
          id='roster_7'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com'
                name='Nurse'>
            <group>[ ... some-very-long-group-name ... ]</group>
          </item>
        </query>
      </iq>

   S: <iq id='roster_7'
          to='juliet@example.com/balcony' type='error' id='roster_7'>
          type='error'>
        <error type='modify'>
          <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
        </error>
      </iq>

   The server MUST return a <not-allowed/> stanza error to the client if
   the value of the <item/> element's 'jid' attribute matches the bare
   JID <node@domain> portion of the <iq/> element's 'from' attribute
   (i.e., a JID must not MUST NOT be allowed to add itself to its own roster).

   Error: Roster set contains sender's JID

   C: <iq from='juliet@example.com/balcony' type='set' id='roster_8'>
          id='roster_8'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='juliet@example.com'/>
         </query>
       </iq>

   S: <iq id='roster_8'
          to='juliet@example.com/balcony' type='error' id='roster_8'>
          type='error'>
         <error type='cancel'>
           <not-allowed xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
         </error>
       </iq>








Saint-Andre             Expires January 13, 2009               [Page 20]

Internet-Draft                   XMPP IM                       July 2008


2.4.  Updating a Roster Item

2.4.1.  Success Case  Request

   Updating an existing roster item is done in the same way as adding a
   new roster item, i.e., by sending a roster set to the server.
   Because a roster item is atomic, the item shall MUST be updated exactly as
   provided in the roster set.

   There are several reasons why a client might update a roster item:





Saint-Andre             Expires December 8, 2008               [Page 17]

Internet-Draft                   XMPP IM                       June 2008

   1.  Adding a group
   2.  Deleting a group
   3.  Changing the handle
   4.  Deleting the handle

   Consider a roster item that is defined as follows:

       <item jid='romeo@example.net'
             name='Romeo'>
         <group>Friends</group>
       </item>

   The user who has this item in her roster may might want to add the item
   to another group.

   C: <iq from='juliet@example.com/chamber' type='set' id='update_1'> from='juliet@example.com/balcony'
          id='update_1'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='romeo@example.net'
                name='Romeo'>
            <group>Friends</group>
            <group>Lovers</group>
          </item>
        </query>
      </iq>

   The user may might then want to remove the item from the original group.












Saint-Andre             Expires January 13, 2009               [Page 21]

Internet-Draft                   XMPP IM                       July 2008


   C: <iq from='juliet@example.com/chamber' type='set' id='update_2'> from='juliet@example.com/balcony'
          id='update_2'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='romeo@example.net'
                name='Romeo'>
            <group>Lovers</group>
          </item>
        </query>
      </iq>

   The user may might then want to change the handle for the item.

   C: <iq from='juliet@example.com/chamber' type='set' id='update_3'> from='juliet@example.com/balcony'
          id='update_3'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='romeo@example.net'
                name='MyRomeo'>
            <group>Lovers</group>
          </item>
        </query>
      </iq>

   The user may might then want to remove the handle altogether (note:



Saint-Andre             Expires December 8, 2008               [Page 18]

Internet-Draft                   XMPP IM                       June 2008
   including an empty 'name' attribute is equivalent to including no
   'name' attribute).

   C: <iq from='juliet@example.com/chamber' type='set' id='update_4'> from='juliet@example.com/balcony'
          id='update_4'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='romeo@example.net'
                name=''>
            <group>Lovers</group>
          </item>
        </query>
      </iq>

   The user may might then want to remove the item from all groups.

   C: <iq from='juliet@example.com/chamber' type='set' id='update_5'> from='juliet@example.com/balcony'
          id='update_5'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='romeo@example.net'/>
        </query>
      </iq>



Saint-Andre             Expires January 13, 2009               [Page 22]

Internet-Draft                   XMPP IM                       July 2008


2.4.2.  Success Case

   As with adding a roster item, when updating a if the roster item can be successfully
   processed then the server MUST update the roster information in
   persistent storage, send a roster push to all of the user's
   interested resources, and send an IQ result to the initiating
   resource; for details, see Section 2.3.

2.4.2.

2.4.3.  Error Cases

   The error cases described under Section 2.3.2 2.3.3 also apply to updating
   a roster item.

2.5.  Deleting a Roster Item

2.5.1.  Success Case  Request

   At any time, a client may can delete an item from his or her roster by
   sending a roster set and specifying the value of the 'subscription'
   attribute to be "remove".

   C: <iq from='juliet@example.com/balcony' type='set' id='delete_1'>
          id='delete_1'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='nurse@example.com' subscription='remove'/>
        </query>
      </iq>

2.5.2.  Success Case

   As with adding a roster item, if the server can successfully process
   the roster set then it MUST update the roster information in
   persistent storage, send a roster push to all of the user's
   interested resources (with the 'subscription' attribute set to a



Saint-Andre             Expires December 8, 2008               [Page 19]

Internet-Draft                   XMPP IM                       June 2008
   value of "remove"), and send an IQ result to the initiating resource;
   for details, see Section 2.3.

   The

   If the user has a presence subscription to the contact or the contact
   has a presence subscription to the user, the user's server MUST also
   generate a presence stanza of type "unsubscribe"
   and (to unsubscribe from
   the contact's presence) or a presence stanza of type "unsubscribed" from
   (to cancel the user contact's subscription to the
   contact. user), or both.








Saint-Andre             Expires January 13, 2009               [Page 23]

Internet-Draft                   XMPP IM                       July 2008


   S: <presence from='juliet@example.com'
                to='nurse@example.com'
                type='unsubscribe'/>

   S: <presence from='juliet@example.com'
                to='nurse@example.com'
                type='unsubscribed'/>

2.5.2.

2.5.3.  Error Cases

   If the value of the 'jid' attribute specifies an item that is not in
   the roster, the server MUST return an <item-not-found/> stanza error.

   Error: Roster item not found

   C: <iq from='juliet@example.com/balcony'
          type='set'
          id='delete_2'>
          id='delete_2'
          type='set'>
        <query xmlns='jabber:iq:roster'>
          <item jid='[ ... non-existent-jid ... ]'
                subscription='remove'/>
        </query>
      </iq>

   S: <iq id='delete_2'
          to='juliet@example.com/balcony' type='error' id='delete_2'>
          type='error'>
        <error type='modify'>
          <item-not-found xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
        </error>
      </iq>


3.  Managing Presence Subscriptions

   In order to protect the privacy of instant messaging users, presence
   information is disclosed only to other entities that the a user has
   approved.  When a user has agreed that another entity may is allowed to
   view its presence, the entity is said to have a SUBSCRIPTION to the
   user's presence.  An entity that has a subscription to a user's
   presence or to which a user has a presence subscription is called a
   CONTACT (in this document the term "contact" is also used in a less
   strict sense to refer to a potential contact or an item in a user's
   roster).



Saint-Andre             Expires December 8, 2008               [Page 20]

Internet-Draft                   XMPP IM                       June 2008

   In XMPP, a subscription lasts across presence sessions; indeed, it
   lasts until the contact unsubscribes or the user cancels the
   previously-granted subscription.



Saint-Andre             Expires January 13, 2009               [Page 24]

Internet-Draft                   XMPP IM                       July 2008


   Subscriptions are managed within XMPP by sending presence stanzas
   containing specially-defined attributes ("subscribe", "unsubscribe",
   "subscribed", and "unsubscribed").

   Subscription states are reflected in the rosters of both the user and
   the contact.  Complete details regarding these subscription states
   can be found Appendix A; those details are not provided in this
   section, which simply narrates the protocol flows for common use
   cases related to presence subscriptions.

      Note: When a server processes or generates an outbound presence
      stanza of type "subscribe", "subscribed", "unsubscribe", or
      "unsubscribed", the server MUST stamp the outgoing presence stanza
      with the bare JID <node@domain> of the sending entity, not the
      full JID <node@domain/resource>.  This  Enforcement of this rule
      simplifies the presence subscription model and helps to prevent
      presence leaks; for details, see information about presence leaks, refer to the
      security considerations of [XMPP-CORE].

   Subscription states are reflected in the rosters of both the user and
   the contact.  Complete details regarding these subscription states
   can be found Appendix A; those details are not provided in this
   section, which simply narrates the protocol flows for common use
   cases related to presence subscriptions.

3.1.  Requesting a Subscription

   A SUBSCRIPTION REQUEST is a request from a user for authorization to
   permanently subscribe to a contact's presence information;
   syntactically it is a presence stanza whose 'type' attribute has a
   value of "subscribe".  A subscription request is generated by a
   user's client, processed by the (potential) contact's server, and
   acted on by the contact via the contact's client.  The workflow is
   described in the following sections.

      Note: Presence subscription requests are sent to available
      resources, whereas the roster pushes associated with subscription
      state changes are sent to interested resources.  Therefore if a
      resource wishes to receive both subscription requests and roster
      pushes, it MUST both send initial presence and request the roster.

3.1.1.  Client Generation of Outbound Subscription Request

   A user's client generates a subscription request by sending a
   presence stanza of type "subscribe" and specifying a 'to' address of
   the potential contact's bare JID <contact@domain>.

   UC: <presence to='juliet@example.com' type='subscribe'/>

   A user's client SHOULD NOT send

   When a user sends a presence subscription request to a potential
   instant messaging and presence contact, the value of the 'to'
   attribute MUST be a bare JID <contact@domain> rather a full JID
   <contact@domain/resource>.

   Typically the user's client prompts
   <contact@domain/resource>, since the user desired result is for information about the potential contact ("handle" and desired roster group) and
   generates a roster set with that information before sending user
   to receive presence from all of the
   subscription request, but that behavior is recommended rather than
   required. contact's resources, not merely



Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 21] 25]

Internet-Draft                   XMPP IM                       June                       July 2008


   the particular resource specified in the 'to' attribute.  Use of bare
   JIDs also simplifies subscription processing, presence probes, and
   presence notifications by the user's server and the contact's server.

      Although many XMPP clients prompt the user for information about
      the potential contact (e.g., "handle" and desired roster group)
      when generating an outbound presence subscription request, the
      client MUST NOT send a roster set before sending the presence
      subscription request, but instead MUST wait until receiving the
      initial roster push from the server.  This enables the user's
      server to enforce any policies relevant to presence subscriptions
      (e.g., a prohibition on presence subscriptions to full JIDs).

3.1.2.  Server Processing of Outbound Subscription Request

   As mentioned,

   Upon receiving the outbound presence subscription request, the user's
   server MUST stamp proceed as follows.

   1.  Before processing the outbound subscription
   request with request, the bare JID <user@domain> user's server SHOULD check the
       syntax of the user.

   US: <presence from='romeo@example.net'
                 to='juliet@example.com'
                 type='subscribe'/>

   Note: JID contained in the 'to' attribute.  If the subscription request is directed to a full JID is
       of the form <contact@domain/resource> instead of a bare JID
       <contact@domain>, the user's server MAY SHOULD treat it as if the
       request had been directed to the contact's bare JID and modify
       the 'to' address accordingly.  This
   simplifies processing of presence subscriptions.  The server MAY also verify that
       the JID adheres to the format defined in [XMPP-CORE], including
       checking against the relevant stringprep profiles.
   2.  If the potential contact is hosted on the same server, server as the
       user, the server MUST adhere to the rules specified in the next
       section in processing the subscription request and delivering it
       to the (local) contact.
   3.  If the potential contact is hosted on a different remote server, subject to
       local service policies the user's server MUST then routes route the
       stanza to that foreign remote domain in accordance with core XMPP stanza
       processing rules.

   The user's server MUST then send a roster push  (This can result in returning an appropriate
       stanza error to all of the user, such as <remote-server-timeout/>.)

   As mentioned, before locally delivering or remotely routing the
   presence subscription request, the user's
   interested resources, containing server MUST stamp the potential contact with a
   outbound subscription state of "none" and request with notation that the subscription bare JID <user@domain> of the
   user.

   US: <presence from='romeo@example.net'
                 to='juliet@example.com'
                 type='subscribe'/>

   After locally delivering or remotely routing the presence
   subscription request, the user's server MUST then send a roster push
   to all of the user's interested resources, containing the potential



Saint-Andre             Expires January 13, 2009               [Page 26]

Internet-Draft                   XMPP IM                       July 2008


   contact with a subscription state of "none" and with notation that
   the subscription is pending (via an 'ask' attribute whose value is
   "subscribe").

   US: <iq id='b89c5r7ib574'
           to='romeo@example.net/foo'
           type='set'
           id='b89c5r7ib574'>
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item ask='subscribe'
                 jid='juliet@example.com'
                 subscription='none'
                 ask='subscribe'/>
                 subscription='none'/>
         </query>
       </iq>

   US: <iq id='b89c5r7ib575'
           to='romeo@example.net/bar'
           type='set'
           id='b89c5r7ib575'>
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item ask='subscribe'
                 jid='juliet@example.com'
                 subscription='none'
                 ask='subscribe'/>
                 subscription='none'/>
           </item>
         </query>
       </iq>



Saint-Andre             Expires December 8, 2008               [Page 22]

Internet-Draft                   XMPP IM                       June 2008


   Note: Because the server must send this roster push, a client MAY
   simply wait for the roster push rather than proactively adding the
   contact to the user's roster before sending the subscription request.

   Note:

   If the contact does not approve or deny the subscription request
   within some configurable amount of time, the user's server SHOULD re-send re-
   send the subscription request to the contact based on an
   implementation-specific algorithm (e.g., whenever a new resource
   becomes available for the user, or after a certain amount of time has
   elapsed); this helps to recover from transient, silent errors that
   may
   might have occurred in relation to the original subscription request.

3.1.3.  Server Processing of Inbound Subscription Request

   The

   Before processing the inbound presence subscription request, the
   contact's server MUST adhere SHOULD check the syntax of the JID contained in the
   'to' attribute.  If the JID is of the form <contact@domain/resource>
   instead of <contact@domain>, the contact's server SHOULD treat it as
   if the request had been directed to the following rules when contact's bare JID and modify
   the 'to' address accordingly.  The server MAY also verify that the
   JID adheres to the format defined in [XMPP-CORE], including checking
   against the relevant stringprep profiles.

   When processing the inbound presence subscription request: request, the
   contact's server MUST adhere to the following rules:





Saint-Andre             Expires January 13, 2009               [Page 27]

Internet-Draft                   XMPP IM                       July 2008


   1.  Above all, the contact's server MUST NOT automatically approve
       subscription requests on the contact's behalf; instead, if a
       subscription request requires approval then the contact's server
       MUST deliver that request to the contact's interested available resource(s)
       for approval or denial by the contact.
   2.  If the contact does not exist, then the contact's server MUST
       automatically return a presence stanza of type "unsubscribed" to
       the user.

   CS: <presence from='juliet@example.com'
                 to='romeo@example.net'
                 type='unsubscribed'/>

   3.  If the contact exists and the user already has a subscription to
       the user's presence, then the contact's server SHOULD MUST auto-reply on
       behalf of the contact by sending a presence stanza of type
       "subscribed" from the contact's bare JID to the user's bare JID.
       If the contact previously sent a presence stanza of type
       "subscribed" and the contact's server treated that as indicating
       "pre-approval" for the user's presence subscription (see
       Appendix A), then the contact's server MAY SHOULD also auto-reply on
       behalf of the contact.
   4.  If the contact exists, the user does not already have a
       subscription to the contact's presence, and there is at least one
       interested
       available resource associated with the contact when the
       subscription request is received by the contact's server, then
       the contact's server MUST broadcast that subscription request to
       all
       interested available resources in accordance with Server Rules for
       Processing XML Stanzas (Section 8).





Saint-Andre             Expires December 8, 2008               [Page 23]

Internet-Draft                   XMPP IM                       June 2008 Section 8.
   5.  If the contact exists, the user does not already have a
       subscription to the contact's presence, and the contact has no
       interested
       available resources when the subscription request is received by
       the contact's server, then the contact's server MUST keep a
       record of the complete presence stanza comprising the
       subscription request, including any extended content contained
       therein, and deliver the request when the contact next has an interested
       available resource.  The contact's server MUST continue to
       deliver the subscription request whenever the contact creates an interested
       available resource, until the contact either approves or denies
       the request.  (Note: The contact's server MUST NOT deliver more
       than one subscription request from any given user when the
       contact next has an
       interested available resource; e.g., if the user sends
       multiple subscription requests to the contact while the contact
       is offline, the contact's server SHOULD store only one of those
       requests, such as the first request or last request, and MUST
       deliver only one of the requests when the contact next has an
       interested
       available resource; this helps to prevent "subscription request
       spam".)

   Note: If the subscription request is directed to a full JID
   <contact@domain/resource> instead of a bare JID <contact@domain>, the
   contact's server MAY treat it as if the request had been directed to
   the contact's bare JID.  This simplifies processing of presence
   subscriptions.




Saint-Andre             Expires January 13, 2009               [Page 28]

Internet-Draft                   XMPP IM                       July 2008


   Note: Until and unless the contact approves the subscription request
   as described under Section 3.1.4, the contact's server MUST NOT add
   an item for the user to the contact's roster.

3.1.4.  Client Processing of Inbound Subscription Request

   When the contact's client receives a subscription request from the
   user, it MUST present the request to the contact for approval (unless
   the contact has explicitly configured the client to automatically
   approve or deny some or all subscription requests).

   A subscription request is approved by sending a presence stanza of
   type "subscribed", which is processed as described in the following
   sections for both the contact's server and the user's server.

   CC: <presence to='romeo@example.net' type='subscribed'/>

   Note: Before approving a presence subscription, the contact MAY
   generate a roster set that includes a handle for the user and that
   places the user in one or more roster groups; see Section 2.3.

   A subscription request is denied by sending a presence stanza of type



Saint-Andre             Expires December 8, 2008               [Page 24]

Internet-Draft                   XMPP IM                       June 2008
   "unsubscribed", which is processed as described under Section 3.2 for
   both the contact's server and the user's server.

   CC: <presence to='romeo@example.net' type='unsubscribed'/>

3.1.5.  Server Processing of Outbound Subscription Approval

   When the contact's client sends the subscription approval, the
   contact's server MUST stamp the outbound stanza with the bare JID
   <contact@domain> of the contact and route or locally deliver or remotely route
   the stanza to the user.

   CS: <presence from='juliet@example.com'
                 to='romeo@example.net'
                 type='subscribed'/>

   The contact's server then MUST send a roster push to all of the
   contact's interested resources.















Saint-Andre             Expires January 13, 2009               [Page 29]

Internet-Draft                   XMPP IM                       July 2008


   CS: <iq id='a78b4q6ha463'
           to='juliet@example.com/balcony'
           type='set'
           id='a78b4q6ha463'>
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='romeo@example.net'
                 subscription='from'/>
         </query>
       </iq>

   CS: <iq id='a78b4q6ha464'
           to='juliet@example.com/chamber'
           type='set'
           id='a78b4q6ha464'>
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='romeo@example.net'
                 subscription='from'/>
         </query>
       </iq>

   The contact's server MUST then also send current presence to the user
   from each of the contact's available resources.

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'/>

   CS: <presence from='juliet@example.com/chamber'
                 to='romeo@example.net'/>

   From the perspective of the contact, there now exists a subscription
   from the user.



Saint-Andre             Expires December 8, 2008               [Page 25]

Internet-Draft                   XMPP IM                       June 2008

   In order to subscribe to the user's presence, the contact would then
   send a subscription request to the user.  (XMPP clients will often
   automatically send the subscription request instead of requiring the
   contact to initiate the subscription request, since it is assumed
   that the desired end state is a mutual subscription.)  Naturally,
   when the contact sends a subscription request to the user, the
   subscription states will be different from those shown in the
   foregoing examples (see Appendix A) and the roles will be reversed.

3.1.6.  Server Processing of Inbound Subscription Approval

   When the user's server receives the subscription approval, it MUST
   first check if the contact is in the user's roster with a
   subscription='none' or subscription='from' and the 'ask' flag set to
   "subscribe" (i.e., a subscription states state of "None + Pending Out" Out",
   "None + Pending Out+In", or "From + Pending Out"; see Appendix A).
   If the contact is not in the
   user's roster with either of those states, the user's server MUST
   silently ignore the presence stanza of type "subscribed" (i.e., it
   MUST NOT route it to the user, modify the user's roster, or generate
   a roster push to the user's interested resources).

   If the foregoing this check is successful, the user's server MUST initiate a roster
   push to all of the user's interested resources, containing an updated



Saint-Andre             Expires January 13, 2009               [Page 30]

Internet-Draft                   XMPP IM                       July 2008


   roster item for the contact with the 'subscription' attribute set to
   a value of "to". "to" (if the subscription state was "None + Pending Out"
   or "None + Pending Out+In") or "both" (if the subscription state was
   "From + Pending Out").

   US: <iq id='b89c5r7ib576'
           to='romeo@example.net/foo'
           type='set'
           id='b89c5r7ib576'>
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='juliet@example.com'
                 subscription='to'/>
         </query>
       </iq>

   US: <iq id='b89c5r7ib577'
           to='romeo@example.net/bar'
           type='set'
           id='b89c5r7ib577'>
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='juliet@example.com'
                 subscription='to'/>
           </item>
         </query>
       </iq>

   From

   (Otherwise -- that is, if the perspective of user does not exist, if the user, there now exists a subscription to contact is
   not in the contact's presence.




Saint-Andre             Expires December 8, 2008               [Page 26]

Internet-Draft                   XMPP IM                       June 2008


   The user's server MUST roster, or if the contact is in the user's roster
   with a subscription state other than those described in the foregoing
   check -- then the user's server MUST silently ignore the stanza by
   not delivering it to the user, not modifying the user's roster, and
   not generating a roster push to the user's interested resources.)

   From the perspective of the user, there now exists a subscription to
   the contact's presence.

   The user's server MUST also deliver the available presence stanza
   received from each of the contact's available resources to each of
   the user's available resources.














Saint-Andre             Expires January 13, 2009               [Page 31]

Internet-Draft                   XMPP IM                       July 2008


   [ ... to resource1 ... ]

   US: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'/>

   [ ... to resource2 ... ]

   US: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'/>

   [ ... to resource1 ... ]

   US: <presence from='juliet@example.com/chamber'
                 to='romeo@example.net'/>

   [ ... to resource2 ... ]

   US: <presence from='juliet@example.com/chamber'
                 to='romeo@example.net'/>

3.2.  Cancelling a Subscription

3.2.1.  Client Generation of Subscription Cancellation

   If a contact would like to cancel a subscription that it has
   previously granted to a user (or deny a subscription request), it
   sends a presence stanza of type "unsubscribed".

   CC: <presence to='romeo@example.net' type='unsubscribed'/>

3.2.2.  Server Processing of Outbound Subscription Cancellation

   As mentioned,

   Upon receiving the outound subscription cancellation, the contact's
   server MUST stamp the outbound
   subscription cancellation with the bare JID <contact@domain> of the
   contact.

   CS: <presence from='juliet@example.com'
                 to='romeo@example.net'
                 type='unsubscribed'/> proceed as follows.

   1.  If the user is hosted on the same server, server as the contact, the
       server MUST adhere to the rules specified in the next section when in
       processing the subscription cancellation.




Saint-Andre             Expires December 8, 2008               [Page 27]

Internet-Draft                   XMPP IM                       June 2008
   2.  If the user is hosted on a different remote server, subject to local
       service policies the contact's server MUST then routes route the stanza
       to that foreign remote domain in accordance with core XMPP stanza
       processing rules.

   If the user is  (This can result in returning an appropriate
       stanza error to the contact, such as <remote-server-timeout/>.)

   As mentioned, before locally delivering or remotely routing the
   stanza, the contact's roster, server MUST stamp the outbound subscription
   cancellation with the bare JID <contact@domain> of the contact.




Saint-Andre             Expires January 13, 2009               [Page 32]

Internet-Draft                   XMPP IM                       July 2008


   CS: <presence from='juliet@example.com'
                 to='romeo@example.net'
                 type='unsubscribed'/>

   The contact's server then MUST send a roster push with the updated
   roster item to all of the contact's interested resources, where the
   subscription state is now either "none" or "to" (see Appendix A).

   CS: <iq id='a78b4q6ha465'
           to='juliet@example.com/balcony'
           type='set'
           id='a78b4q6ha465'>
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='romeo@example.net'
                 subscription='none'/>
         </query>
       </iq>

   CS: <iq id='a78b4q6ha466'
           to='juliet@example.com/chamber'
           type='set'
           id='a78b4q6ha466'>
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='romeo@example.net'
                 subscription='none'/>
         </query>
       </iq>

3.2.3.  Server Processing of Inbound Subscription Cancellation

   When the user's server receives the inbound subscription
   cancellation, it MUST modify first check if the subscription state and send contact is in the user's
   roster with subscription='to' or subscription='both' (see
   Appendix A).  If this check is successful, the user's server MUST
   initiate a roster push to all of the user's interested resources, where
   containing an updated roster item for the contact with the
   'subscription' attribute set to a value of "none" (if the
   subscription state
   is now either "none" was "To" or "To + Pending In") or "from" (see Appendix A). (if the
   subscription state was "Both").














Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 28] 33]

Internet-Draft                   XMPP IM                       June                       July 2008


   US: <iq id='h37h3u1bv400'
           to='romeo@example.net/foo'
           type='set'
           id='h37h3u1bv400'>
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='juliet@example.com'
                 subscription='none'/>
         </query>
       </iq>

   US: <iq id='h37h3u1bv401'
           to='romeo@example.net/bar'
           type='set'
           id='h37h3u1bv401'>
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='juliet@example.com'
                 subscription='none'/>
           </item>
         </query>
       </iq>

   (Otherwise -- that is, if the user does not exist, if the contact is
   not in the user's roster, or if the contact is in the user's roster
   with a subscription state other than those described in the foregoing
   check -- then the user's server MUST silently ignore the stanza by
   not delivering it to the user, not modifying the user's roster, and
   not generating a roster push to the user's interested resources.)

3.3.  Unsubscribing

3.3.1.  Client Generation of Unsubscribe

   If a user would like to unsubscribe from a contact's presence, it
   sends a presence stanza of type "unsubscribe".

   UC: <presence to='juliet@example.com' type='unsubscribe'/>

3.3.2.  Server Processing of Outbound Unsubscribe

   As mentioned,

   Upon receiving the outbound unsubscribe, the user's server MUST stamp the outbound unsubscribe
   with the bare JID <user@domain> of the user.

   US: <presence from='romeo@example.net'
                 to='juliet@example.com'
                 type='unsubscribe'/>
   proceed as follows.

   1.  If the contact is hosted on the same server, server as the user, the
       server MUST adhere to the rules specified in the next section when in
       processing the
   unsubscribe. subscription request.
   2.  If the contact is hosted on a different remote server, subject to local
       service policies the user's server MUST then routes route the stanza to
       that foreign remote domain in accordance with core XMPP stanza processing
       rules.  (This can result in returning an appropriate stanza error
       to the user, such as <remote-server-timeout/>.)



Saint-Andre             Expires January 13, 2009               [Page 34]

Internet-Draft                   XMPP IM                       July 2008


   As mentioned, before locally delivering or remotely routing the
   unsubscrbe, the user's server MUST stamp the stanza with the bare JID
   <user@domain> of the user.

   US: <presence from='romeo@example.net'
                 to='juliet@example.com'
                 type='unsubscribe'/>

   The user's server then MUST send a roster push with the updated
   roster item to all of the user's interested resources, where the
   subscription state is now either "none" or "from" (see Appendix A).



Saint-Andre             Expires December 8, 2008               [Page 29]

Internet-Draft                   XMPP IM                       June 2008

   US: <iq id='h37h3u1bv402'
           to='romeo@example.net/foo'
           type='set'
           id='h37h3u1bv402'>
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='juliet@example.com'
                 subscription='none'/>
         </query>
       </iq>

   US: <iq to='romeo@example.net/bar'
           type='set'
           id='h37h3u1bv403'>
         <query xmlns='jabber:iq:roster'>
           <item jid='juliet@example.com'
                 subscription='none'/>
           </item>
         </query>
       </iq>

3.3.3.  Server Processing of Inbound Unsubscribe

   When the contact's server receives the inbound unsubscribe, subscription approval, it MUST
   modify
   first check if the user is in the contact's roster with
   subscription='from' or subscription='both' (i.e., a subscription
   state and send of "From", "From + Pending Out", or "Both"; see Appendix A).
   If this check is successful, the contact's server MUST initiate a
   roster push to all of the contact's interested resources, where containing
   an updated roster item for the contact with the 'subscription'
   attribute set to a value of "none" (if the subscription state is now either
   "none" was
   "From" or "From + Pending Out") or "to" (see Appendix A). (if the subscription state
   was "Both").








Saint-Andre             Expires January 13, 2009               [Page 35]

Internet-Draft                   XMPP IM                       July 2008


   CS: <iq id='a78b4q6ha467'
           to='juliet@example.com/balcony'
           type='set'
           id='a78b4q6ha467'>
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='romeo@example.net'
                 subscription='none'/>
         </query>
       </iq>

   CS: <iq id='a78b4q6ha468'
           to='juliet@example.com/chamber'
           type='set'
           id='a78b4q6ha468'>
           type='set'>
         <query xmlns='jabber:iq:roster'>
           <item jid='romeo@example.net'
                 subscription='none'/>
         </query>
       </iq>








Saint-Andre             Expires December 8, 2008               [Page 30]

Internet-Draft                   XMPP IM                       June 2008

   (Otherwise -- that is, if the contact does not exist, if the user is
   not in the contact's roster, or if the user is in the contact's
   roster with a subscription state other than those described in the
   foregoing check -- then the contact's server MUST silently ignore the
   stanza by not delivering it to the contact, not modifying the
   contact's roster, and not generating a roster push to the contact's
   interested resources.)


4.  Exchanging Presence Information

4.1.  Overview

   The concept of presence refers to an entity's availability for
   communication over a network.  At the most basic level, presence is a
   boolean "on/off" variable that signals whether an entity is available
   or unavailable for communication (the terms "online" and "offline"
   are also used).  In XMPP, a principal's user's availability is signalled when a
   client controlled by the principal user generates a <presence/> stanza with no
   'type' attribute, and an entity's lack of availability is signalled
   when a client generates a <presence/> stanza whose 'type' attribute
   has a value of "unavailable".  In XMPP-based
   applications that combine messaging and presence functionality, the
   default type of communication for which presence signals availability
   is messaging; however, XMPP-based applications are not required to
   combine messaging and presence functionality, and can provide
   standalone presence features without messaging (in addition, XMPP
   servers do not require information about network availability in
   order to successfully route message and IQ stanzas).

   XMPP presence typically follows a "publish-subscribe" or "observer"
   pattern, wherein an entity sends presence to its server, and its
   server then broadcasts that information to all of the entity's
   contacts who have a subscription to the entity's presence (in the
   terminology of [IMP-MODEL], an entity that generates presence is a
   "presentity" and the entities that receive presence are
   "subscribers").  A client generates presence for broadcasting to all



Saint-Andre             Expires January 13, 2009               [Page 36]

Internet-Draft                   XMPP IM                       July 2008


   subscribed entities by sending a presence stanza to its server with
   no 'to' address, where the presence stanza has either no 'type'
   attribute or a 'type' attribute whose value is "unavailable".  This
   kind of presence is called BROADCASTED BROADCAST PRESENCE.  (A client MAY can also
   send DIRECTED PRESENCE, i.e., a presence stanza with a 'to' address;
   this is less common but is sometimes used to send presence to
   entities that are not subscribed to the principal's user's presence; see
   Section 4.6.)

   After a client completes the preconditions specified in [XMPP-CORE],
   it can establish a PRESENCE SESSION at its server by sending initial
   presence (Section 4.2).  Such a 4.2), where the presence session is terminated by
   sending unavailable presence (Section 4.5).

4.2.  Initial Presence

4.2.1.  Client Generation  For the duration of Initial Presence

   After completing its
   presence session, a connected resource (in the preconditions described in [XMPP-CORE]
   (REQUIRED) terminology of
   [XMPP-CORE]) is said to be an AVAILABLE RESOURCE.

   In XMPP-based applications that combine messaging and requesting presence
   functionality, the roster (RECOMMENDED), a client SHOULD



Saint-Andre             Expires December 8, 2008               [Page 31]

Internet-Draft                   XMPP IM                       June 2008


   signal its availability for default type of communication by for which presence
   signals availability is messaging; however, it is not necessary for
   XMPP-based applications to combine messaging and presence
   functionality, and can provide standalone presence features without
   messaging (in addition, XMPP servers do not require information about
   network availability in order to successfully route message and IQ
   stanzas).

      Note: In the following examples, the "user" is juliet@example.com
      and the user has three contacts in her roster with a subscription
      state of "from" or "both": romeo@example.net,
      mercutio@example.com, and benvolio@example.net.

4.2.  Initial Presence

4.2.1.  Client Generation of Initial Presence

   After completing the preconditions described in [XMPP-CORE]
   (REQUIRED) and requesting the roster (RECOMMENDED), a client signals
   its availability for communication by sending INITIAL PRESENCE to its
   server, i.e., a presence stanza with no 'to' address (indicating that
   it is meant to be broadcasted broadcast by the server on behalf of the client)
   and no 'type' attribute (indicating the user's availability).  After sending

   UC: <presence/>

   The initial presence, a connected resource
   (in presence stanza MAY contain the terminology <priority/> element, the
   <show/> element, and one or more instances of [XMPP-CORE]) is said to be an AVAILABLE
   RESOURCE.

   UC: <presence/> the <status/> element,
   as well as extended content.





Saint-Andre             Expires January 13, 2009               [Page 37]

Internet-Draft                   XMPP IM                       July 2008


4.2.2.  Server Processing of Outbound Presence

   Upon receiving initial presence from a client, the user's server MUST
   send the initial presence stanza from the full JID
   <user@domain/resource> of the user to all contacts that are
   subscribed to the user's presence; such contacts are those for which
   a JID is present in the user's roster with the 'subscription'
   attribute set to a value of "from" or "both".

   Note: In the following examples, the "user" is juliet@example.com and
   the user has three contacts in her roster with a subscription state
   of "from" or "both": romeo@example.net, mercutio@example.com, and
   benvolio@example.com.

   US: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'/>

   US: <presence from='juliet@example.com/balcony'
                 to='mercutio@example.com'/>

   US: <presence from='juliet@example.com/balcony'
                 to='benvolio@example.com'/>
                 to='benvolio@example.net'/>

   The user's server MUST also broadcast initial presence from the
   user's newly available resource to all of the user's available
   resources.
   resources (including the resource that generated the presence
   notification in the first place).

   US: <presence from='juliet@example.com/balcony'
                 to='juliet@example.com/balcony'/>

   US: <presence from='juliet@example.com/balcony'
                 to='juliet@example.com/chamber'/>

   In the absence of presence information about the user's contacts, the
   user's server SHOULD MUST also send presence probes to the user's contacts
   on behalf of the user as specified under Section 4.3.





Saint-Andre             Expires December 8, 2008               [Page 32]

Internet-Draft                   XMPP IM                       June 2008

4.2.3.  Server Processing of Inbound Presence

   Upon receiving presence from the user, the contact's server MUST
   deliver the user's presence stanza to all of the contact's available
   resources.

   [ ... to resource1 ... ]

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'/>

   [ ... to resource2 ... ]

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'/>



Saint-Andre             Expires January 13, 2009               [Page 38]

Internet-Draft                   XMPP IM                       July 2008


   If there is no such contact, the contact's server MUST silently
   ignore the presence stanza.

4.2.4.  Client Processing of Inbound Presence

   When the contact's client receives presence from the user and user, it SHOULD
   proceed as follows:

   1.  If the user is in the contact's roster, it SHOULD the client MUST display
       the presence information in an appropriate roster interface.
   2.  If the user is not in the contact's roster but the contact and
       the user are actively exchanging message or IQ stanzas, the
       contact's client SHOULD display the presence information in the
       user interface for that chat session (see also Section 4.6 and
       Section 5.4). 5.1).
   3.  Otherwise, the client SHOULD MUST ignore the presence information and
       not display it to the contact.

4.3.  Presence Probes

   A PRESENCE PROBE is a request for a contact's current presence
   information, sent on behalf of a user by the user's server;
   syntactically it is a presence stanza whose 'type' attribute has a
   value of "probe".  The value of the 'from' address SHOULD MUST be the full
   JID <user@domain/resource> of the probing user and the value of the 'to'
   address SHOULD MUST be the bare JID <contact@domain> of the contact
   whose availability to which
   the user wants to discover. is subscribed.

   US: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'
                 type='probe'/>

   A presence probe SHOULD NOT be sent by a client.  Instead, it is
   designed to be sent by a user's server on the user's behalf in order
   to discover the availability of the user's contacts.

   If a server receives a presence probe intended for a full JID
   <contact@domain/resource>, it SHOULD treat the probe as if the 'to'



Saint-Andre             Expires December 8, 2008               [Page 33]

Internet-Draft                   XMPP IM                       June 2008
   address was a bare JID, but MAY instead handle it on behalf of the
   connected resource by returning only the presence information for
   that particular resources (and in any case MUST NOT deliver it to the
   resource).

4.3.1.  Server Generation of Outbound Presence Probe

   When a server needs to discover the availability of a user's contact,
   it SHOULD send sends a presence probe from the full JID <user@domain/resource> of
   the user to the bare JID <contact@domain> of the contact.  The server SHOULD



Saint-Andre             Expires January 13, 2009               [Page 39]

Internet-Draft                   XMPP IM                       July 2008


   MUST NOT send a probe to a contact only if the user is not subscribed to
   the contact's presence (i.e., if the contact is not in the user's
   roster with the 'subscription' attribute set to a value of "to" or "both" (i.e., if the user is subscribed to
   the contact's presence).
   "both".

   The user's server SHOULD send a presence probe whenever the user
   starts a new presence session by sending initial presence; however,
   the server MAY choose not to send the probe at that point if it has
   what it deems to be reliable and up-to-date presence information
   about the user's contacts (e.g., because the user has another
   available resource or because the user briefly logged off and on
   before the new presence session began).  In addition, a server MAY
   periodically send a presence probe to a contact if it has not
   received presence information or other traffic from the contact in
   some configurable amount of time; this can help to prevent "ghost"
   contacts who appear to be online but in fact are not.

   US: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'
                 type='probe'/>

   US: <presence from='juliet@example.com/balcony'
                 to='benvolio@example.com'
                 type='probe'/>

   US: <presence from='juliet@example.com/balcony'
                 to='nurse@example.com'
                 to='benvolio@example.net'
                 type='probe'/>

   Naturally, the user's server does not need to send a presence probe
   to a contact if the contact's account resides on the same server as
   the user, since the server possesses contact's information locally.

4.3.2.  Server Processing of Inbound Presence Probe

   Upon receiving a presence probe from the user's server on behalf of
   the user, the contact's server SHOULD reply as follows:

   1.  If the contact account does not exist or the user is in the
       contact's roster with a subscription state other than "From",
       "From + Pending Out", or "Both" (as defined under Appendix A),
       the contact's server MUST return a presence stanza of type



Saint-Andre             Expires December 8, 2008               [Page 34]

Internet-Draft                   XMPP IM                       June 2008
       "unsubscribed" in response to the presence probe (however, if a
       server receives a presence probe from a configured hostname of
       the server itself or another such trusted service, it MAY provide
       presence information about the user to that entity).

   CS: <presence from='mercutio@example.com'
                 to='juliet@example.com'
                 type='unsubscribed'/>





Saint-Andre             Expires January 13, 2009               [Page 40]

Internet-Draft                   XMPP IM                       July 2008


   2.  Else, if the contact has no available resources, the server
       SHOULD reply to the presence probe by sending to the user the
       full XML of the last presence stanza of type "unavailable"
       received by the server from the contact (but (however, the server MAY
       opt to not reply at all).
   3.  Else, if the contact has at least one available resource, the
       server MUST reply to the presence probe by sending to the user
       the full XML of the last presence stanza with no 'to' attribute
       received by the server from each of the contact's available
       resources.

   CS: <presence from='romeo@example.net/foo'
                 to='juliet@example.com'/>

   CS: <presence from='romeo@example.net/bar'
                 to='juliet@example.com'>
         <show>away</show>
       </presence>

4.4.  Subsequent Presence Broadcast

4.4.1.  Client Generation of Presence Broadcast

   After sending initial presence, the user's client may can update its
   availability for broadcasting at any time during its session by
   sending a presence stanza with no 'to' address and no 'type'
   attribute.

   UC: <presence>
         <show>away</show>
       </presence>

   Note: A

   The presence broadcast MAY contain the <priority/> element, the
   <show/> element, and one or more instances of the <status/> element,
   as well as extended content.

   However, a user SHOULD NOT send a presence update only to broadcast
   information that changes independently of is relevant to the user's availability for
   communication.







Saint-Andre             Expires December 8, 2008               [Page 35]

Internet-Draft
   communication or the communication capabilities of the connected
   resource.  Information that is not relevant in this way can be of
   interest to the user's contacts but SHOULD be sent via other means,
   such as the XMPP IM                       June 2008 message stanza.

4.4.2.  Server Processing of Outbound Presence

   Upon receiving a presence stanza expressing updated availability, the
   user's server MUST broadcast the full XML of that presence stanza to
   the contacts who meet all of the following criteria:



Saint-Andre             Expires January 13, 2009               [Page 41]

Internet-Draft                   XMPP IM                       July 2008


   1.  The contact is in the user's roster with a subscription type of
       "from" or "both".
   2.  The last presence stanza received from the contact during the
       user's presence session was not of type "error" or "unsubscribe".

   As an optimization, if the subscription type is "both", the server
   MAY
   SHOULD send subsequent presence notifications to a contact only if
   the contact is online according to the user's server.  That is, if
   the user's server never received a positive indication that the
   contact is online in response to the presence probe it sent to the
   contact or if the last presence stanza it received from the contact
   during the user's presence session was of type "unavailable", the
   user's server
   MAY opt not to SHOULD NOT send subsequent presence notifications from
   the user to the contact.

   US: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'>
         <show>away</show>
       </presence>

   US:  This optimization helps to save bandwidth,
   since most presence subscriptions are bidirectional and many contacts
   will not be online at any given time.

   US: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'>
         <show>away</show>
       </presence>

   US: <presence from='juliet@example.com/balcony'
                 to='benvolio@example.com'>
                 to='benvolio@example.net'>
         <show>away</show>
       </presence>

   US: <presence from='juliet@example.com/balcony'
                 to='mercutio@example.com'>
         <show>away</show>
       </presence>

      See Section 4.6 regarding rules that supplement the foregoing for
      handling of directed presence.

   The user's server MUST also send the presence stanza to all of the
   user's available resources. resources (including the resource that generated the
   presence notification in the first place).

   US: <presence from='juliet@example.com/balcony'
                 to='juliet@example.com/chamber'>
         <show>away</show>
       </presence>

   US: <presence from='juliet@example.com/balcony'
                 to='juliet@example.com/balcony'>
         <show>away</show>
       </presence>



Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 36] 42]

Internet-Draft                   XMPP IM                       June                       July 2008


4.4.3.  Server Processing of Inbound Presence

   Upon receiving presence from the user, the contact's server MUST
   deliver the user's presence stanza to all of the contact's available
   resources.

   [ ... to resource1 ... ]

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'>
         <show>away</show>
       </presence>

   [ ... to resource2 ... ]

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'>
         <show>away</show>
       </presence>

4.4.4.  Client Processing of Inbound Presence

   When the contact's client receives presence from the user and user, it SHOULD
   proceed as follows:

   1.  If the user is in the contact's roster, it SHOULD the client MUST display
       the presence information in an appropriate roster interface.
   2.  If the user is not in the contact's roster but the contact and
       the user are actively exchanging message or IQ stanzas, the
       contact's client SHOULD display the presence information in the
       user interface for that chat session (see also Section 4.6 and
       Section 5.4). 5.1).
   3.  Otherwise, the client SHOULD MUST ignore the presence information and
       not display it to the contact.

4.5.  Unavailable Presence

4.5.1.  Client Generation of Unavailable Presence

   Before ending its presence session with a server, the user's client
   SHOULD gracefully become unavailable by sending UNAVAILABLE PRESENCE,
   i.e., a presence stanza that possesses no 'to' attribute and that
   possesses a 'type' attribute whose value is "unavailable".

   UC: <presence type='unavailable'/>

   Optionally, the final unavailable presence stanza MAY contain one or more
   <status/> elements specifying the reason why the user is no longer
   available.



Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 37] 43]

Internet-Draft                   XMPP IM                       June                       July 2008


   available.

   US: <presence type='unavailable'>
         <status>going on vacation</status>
       </presence>

   However, the unavailable presence stanza MUST NOT contain the
   <priority/&Gt; element or the <show/> element, since these elements
   apply only to available presence.

4.5.2.  Server Processing of Outbound Unavailable Presence

   The user's server MUST NOT depend on receiving unavailable presence
   from an available resource, since the resource may can become unavailable
   ungracefully (e.g., the resource may can be timed out by the server
   because of inactivity).

   If an available resource becomes unavailable for any reason (either
   gracefully or ungracefully), the user's server MUST broadcast
   unavailable presence to all contacts that meet all of the following
   criteria:

   1.  The contact is in the user's roster with a subscription type of
       "from" or "both".
   2.  The last presence stanza received from the contact during the
       user's presence session was not of type "error" or "unsubscribe".

   As an optimization, if the subscription type is "both", the server
   MAY send

      See Section 4.6 regarding rules that supplement the unavailable foregoing for
      handling of directed presence.

      The optimization employed for subsequent presence notification to broadcast during
      a contact only if
   the contact is online according to the user's server.  That is, if
   the user's server never received a positive indication that the
   contact is online in response to the presence probe it sent to the
   contact or session MUST NOT be employed for unavailable
      presence broadcast; if it were, the last presence stanza received from by the contact
   during
      contact's server would be the user's initial presence session was of type "unavailable", the
   user's server MAY opt not to send for the unavailable
      presence
   notification from the user to session, with the contact.

   See Section 4.6 regarding rules result that supplement the foregoing. contact would consider
      the user to be online.

   If the unavailable presence stanza was gracefully received from the
   client, the server MUST broadcast the full XML of the presence
   stanza.











Saint-Andre             Expires January 13, 2009               [Page 44]

Internet-Draft                   XMPP IM                       July 2008


   US: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'
                 type='unavailable'/>
         <status>going on vacation</status>
       </presence>

   US: <presence from='juliet@example.com/balcony'
                 to='benvolio@example.com'
                 type='unavailable'/>
                 to='benvolio@example.net'
                 type='unavailable'>
         <status>going on vacation</status>
       </presence>

   US: <presence from='juliet@example.com/balcony'
                 to='mercutio@example.com'
                 type='unavailable'/>



Saint-Andre             Expires December 8, 2008               [Page 38]

Internet-Draft                   XMPP IM                       June 2008
                 type='unavailable'>
         <status>going on vacation</status>
       </presence>

   The user's server MUST also send the unavailable presence stanza to
   all of the user's remaining available resources.

   US: <presence from='juliet@example.com/balcony'
                 to='juliet@example.com/chamber'
                 type='unavailable'/>
                 type='unavailable'>
         <status>going on vacation</status>
       </presence>

   If the server detects that the user has gone offline ungracefully,
   the server MUST generate the unavailable presence broadcast on the
   user's behalf.

   Note: Any presence stanza with no 'type' attribute and no 'to'
   attribute that is sent after sending broadcasted unavailable presence broadcast
   MUST be broadcasted sent by the user's server to all subscribers (i.e., MUST be
   treated as equivalent to "initial presence" initial presence for a new presence
   session).

4.5.3.  Server Processing of Inbound Unavailable Presence

   Upon receiving unavailable presence from the user, the contact's
   server MUST deliver the user's presence stanza to all of the
   contact's available resources.









Saint-Andre             Expires January 13, 2009               [Page 45]

Internet-Draft                   XMPP IM                       July 2008


   [ ... to resource1 ... ]

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'
                 type='unavailable'/>
                 type='unavailable'>
         <status>going on vacation</status>
       </presence>

   [ ... to resource2 ... ]

   CS: <presence from='juliet@example.com/balcony'
                 to='romeo@example.net'
                 type='unavailable'/>
                 type='unavailable'>
         <status>going on vacation</status>
       </presence>

   If the contact's server is optimizing subsequent presence delivery as
   described under Section 4.4, it SHOULD MUST also note that the user is
   unavailable and appropriately update its internal representation of
   which users entities are online.

4.5.4.  Client Processing of Inbound Unavailable Presence

   When the contact's client receives unavailable presence from the user
   and
   user, it SHOULD proceed as follows:

   1.  If the user is in the contact's roster, it SHOULD the client MUST display
       the unavailable presence information in an appropriate roster
       interface.
   2.  If the user is not in the contact's roster but the contact and
       the user are actively exchanging message or IQ stanzas, the
       contact's client SHOULD display the unavailable presence
       information in the user interface for that chat session (see also
       Section 4.6 and Section 5.4).




Saint-Andre             Expires December 8, 2008               [Page 39]

Internet-Draft                   XMPP IM                       June 2008 5.1).
   3.  Otherwise, the client SHOULD MUST ignore the unavailable presence
       information and not display it to the contact.

4.6.  Directed Presence

   This section supplements and in some respects modifies the rules
   defined above, for
   client and server processing of presence notifications, but only for
   the special case of directed presence.

4.6.1.  Client Generation of Directed Presence

   As noted, directed presence is a presence stanza with a 'to'
   attribute whose value is the bare JID or full JID of the other entity
   and with either no 'type' attribute (indicating availability) or a



Saint-Andre             Expires January 13, 2009               [Page 46]

Internet-Draft                   XMPP IM                       July 2008


   'type' attribute whose value is "unavailable".

   Information about the use of directed presence in the context of a
   one-to-one chat session is provided under Section 5.4. 5.1.

4.6.2.  Server Processing of Outbound Directed Presence

   When the user's server receives the a directed presence stanza, it SHOULD
   process it according to the following rules.

   1.  If the user sends directed available or unavailable presence to a
       contact that is in the user's roster with a subscription type of
       "from" or "both" after having sent initial presence and before
       sending broadcasted unavailable presence broadcast (i.e., during the user's
       presence session), the user's server MUST route or locally deliver or
       remotely route the full XML of that presence stanza but SHOULD
       NOT otherwise modify the contact's status regarding broadcasted 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 broadcasted unavailable
       presence broadcast (i.e., during the user's presence session),
       the user's server MUST route or locally deliver or remotely route the full
       XML of that presence stanza to the entity but MUST NOT modify the
       contact's status regarding available presence broadcast (i.e., it
       MUST NOT include the entity's JID in any subsequent broadcasts of
       available presence initiated by the user); however, if the
       available resource from which the user sent the directed presence
       become unavailable, the user's server MUST route that unavailable
       presence to the entity (if the user has not yet sent directed
       unavailable presence to that entity).
   3.  If the user sends directed presence without first sending initial
       presence or after having sent unavailable presence broadcast
       (i.e., the resource is connected but not available), the user's



Saint-Andre             Expires December 8, 2008               [Page 40]

Internet-Draft                   XMPP IM                       June 2008
       server MUST treat the entities entity to which the user sends directed
       presence in the same way that it treats the entities listed as in case #2 above.

4.6.3.  Server Processing of Inbound Directed Presence

   From the perspective of the contact's server, there is no difference
   between broadcasted presence broadcast and directed presence, so the contact's
   server follows the existing rules for processing of inbound presence.

4.6.4.  Client Processing of Inbound Directed Presence

   When the contact's client receives directed presence from the user and user,
   it SHOULD proceed as follows:



Saint-Andre             Expires January 13, 2009               [Page 47]

Internet-Draft                   XMPP IM                       July 2008


   1.  If the user is in the contact's roster, it SHOULD the client MUST display
       the presence information in an appropriate roster interface.
   2.  If the user is not in the contact's roster but the contact and
       the user are actively exchanging message or IQ stanzas, the
       contact's client SHOULD display the presence information in an appropriate the
       user
   interface. interface for that chat session (see also Section 4.6 and
       Section 5.1).
   3.  Otherwise, the client SHOULD MUST ignore the presence information and
       not display it to the contact.

4.7.  Presence Syntax

4.7.1.  Type Attribute

   The absence of a 'type' attribute signals that the relevant entity is
   available for communication (see Section 4.2 and Section 4.4).

   A 'type' attribute with a value of "unavailable" signals that the
   relevant entity is not available for communication (see Section 4.5).

   The XMPP presence stanza is also used to negotiate and manage
   subscriptions to the presence of other entities.  These tasks are
   completed via presence stanzas of type "subscribe", "unsubscribe",
   "subscribed", and "unsubscribed" as described under Section 3.

   If a user and contact are associated with different XMPP servers,
   those servers also use a special presence stanza of type "probe" in
   order to determine the availability of the entity on the peer server;
   for details, see Section 4.3.  Clients SHOULD NOT send presence
   stanzas of type "probe".

   The values of the 'type' attribute can be summarized as follows:





Saint-Andre             Expires December 8, 2008               [Page 41]

Internet-Draft                   XMPP IM                       June 2008

   o  error -- An error has occurred regarding processing of a
      previously-sent presence stanza; if the presence stanza is of type
      "error", it MUST include an <error/> child element (refer to
      [XMPP-CORE]).
   o  probe -- A request for an entity's current presence; SHOULD be
      generated only by a server on behalf of a user.
   o  subscribe -- The sender wishes to subscribe to the recipient's
      presence.
   o  subscribed -- The sender has allowed the recipient to receive
      their presence.
   o  unavailable -- Signals that the entity is no longer available for
      communication.
   o  unsubscribe -- The sender is unsubscribing from another entity's the receiver's
      presence.




Saint-Andre             Expires January 13, 2009               [Page 48]

Internet-Draft                   XMPP IM                       July 2008


   o  unsubscribed -- The subscription request has been denied or a
      previously-granted subscription has been cancelled.
   o  unavailable -- Signals that the entity is no longer available for
      communication.

   If

   If the value of the 'type' attribute is not one of the foregoing
   values, the recipient or an intermediate router SHOULD return a
   stanza error of <bad-request/>.

      Note: There is no default value for the 'type' attribute of the
      <presence/> element.  Therefore if the intended recipient or
   intermediate router receives a <presence/> element whose 'type' value element; in particular, there is undefined, it SHOULD return a stanza error no value of <bad-request/>.
      "available".

4.7.2.  Child Elements

   In accordance with the default namespace declaration, a presence
   stanza is qualified by the 'jabber:client' or 'jabber:server'
   namespace, which defines certain allowable children of presence
   stanzas, in particular the <show/>, <status/>, and <priority/>
   elements.  These child elements are used to provide more detailed
   information about an entity's availability.  Typically these child
   elements are provided only if the presence stanza possesses no 'type'
   attribute, although exceptions are noted in the text that follows.

4.7.3.  Show Element

   The OPTIONAL <show/> element specifies the particular availability
   sub-state of an entity or a specific resource thereof.  A presence
   stanza MUST NOT contain more than one <show/> element.  The <show/>
   element MUST NOT possess any attributes.  The XML character data of
   the <show/> element is not human-readable.  The XML character data
   MUST be one of the following (additional availability states could be
   defined through a properly-namespaced child element of the presence
   stanza):




Saint-Andre             Expires December 8, 2008               [Page 42]

Internet-Draft                   XMPP IM                       June 2008 stanza that is
   qualified by a namespace other than the default namespace):

   o  away -- The entity or resource is temporarily away.
   o  chat -- The entity or resource is actively interested in chatting.
   o  dnd -- The entity or resource is busy (dnd = "Do Not Disturb").
   o  xa -- The entity or resource is away for an extended period (xa =
      "eXtended Away").

   If no <show/> element is provided, the entity is assumed to be online
   and available.

   Any specialized processing of availability states by recipients and
   intermediate routers is up to the implementation (e.g., incorporation
   of availability states into server stanza routing and delivery logic).






Saint-Andre             Expires January 13, 2009               [Page 49]

Internet-Draft                   XMPP IM                       July 2008


4.7.4.  Status Element

   The OPTIONAL <status/> element contains human-readable XML character
   data specifying a natural-language description of an entity's
   availability.  It is normally used in conjunction with the show
   element to provide a detailed description of an availability state
   (e.g., "In a meeting") when the presence stanza has no 'type'
   attribute.

   <presence from='romeo@example.net/orchard'
             xml:lang='en'>
     <show>dnd</show>
     <status>Wooing Juliet</status>
   </presence>

   The <status/> element MUST NOT possess any attributes, with the
   exception of the 'xml:lang' attribute.  Multiple instances of the
   <status/> element MAY be included, but only if each instance
   possesses an 'xml:lang' attribute with a distinct language value
   (either explicitly or by inheritance from the 'xml:lang' value of an
   element farther up in the XML hierarchy, which may can include the XML
   stream header as described in [XMPP-CORE]).

   <presence from='romeo@example.net/orchard'
             xml:lang='en'>
     <show>dnd</show>
     <status>Wooing Juliet</status>
     <status xml:lang='cs'>Dvo&#x0159;&#x00ED;m se Julii</status>
   </presence>

   A presence stanza of type "unavailable" MAY also include a <status/>
   element to provide detailed information about why the entity is going
   offline.





Saint-Andre             Expires December 8, 2008               [Page 43]

Internet-Draft                   XMPP IM                       June 2008

   <presence from='romeo@example.net/orchard'
             type='unavailable'>
             type='unavailable'
             xml:lang='en'>
     <status>Busy IRL</status>
   </presence>

   The <status/> child MAY also be sent in a subscription-related
   presence stanza (i.e., type "subscribe", "subscribed", "unsubscribe",
   or "unsubscribed") to provide a description of the action.  The
   receiving client MAY present this <status/> information to a human
   user (see Section 11).






Saint-Andre             Expires January 13, 2009               [Page 50]

Internet-Draft                   XMPP IM                       July 2008


   <presence from='romeo@example.net'
             to='nurse@example.com'
             type='subscribe'>
     <status>Hi, Juliet said I should told to add you to my buddy list.</status>
   </presence>

4.7.5.  Priority Element

   The OPTIONAL <priority/> element contains non-human-readable XML
   character data that specifies the priority level of the resource.
   The value MUST be an integer between -128 and +127.  A presence
   stanza MUST NOT contain more than one <priority/> element.  The
   <priority/> element MUST NOT possess any attributes.

   <presence xml:lang='en'>
     <show>dnd</show>
     <status>Wooing Juliet</status>
     <status xml:lang='cs'>Dvo&#x0159;&#x00ED;m se Julii</status>
     <priority>1</priority>
   </presence>

   If no priority is provided, the processing server or client SHOULD MUST
   consider the priority to be zero. zero ("0").

   For information regarding the semantics of priority values in stanza
   processing within instant messaging and presence applications, refer
   to Server Rules for Processing XML Stanzas (Section 8). Section 8.

4.7.6.  Extended Content

   As described in [XMPP-CORE], an XML stanza MAY contain any properly-
   namespaced child element;
   element that is qualified by a namespace other than the default
   namespace; this applies to the presence stanza as well.

   (In the following example, the presence stanza includes entity
   capabilities information as defined in [XEP-0115]).)




Saint-Andre             Expires December 8, 2008               [Page 44]

Internet-Draft                   XMPP IM                       June 2008

   <presence from='romeo@example.net'>
     <c xmlns='http://jabber.org/protocol/caps'
        node='http://psi-im.org/caps'
        ver='0.11'/>
        hash='sha-1'
        node='http://psi-im.org'
        ver='q07IKJEyjvHSyhy//CH0CxmKi8w='/>
   </presence>

   Any extended content included in a presence stanza SHOULD represent
   aspects of an entity's availability for communication or provide
   information about communication-related capabilities.




Saint-Andre             Expires January 13, 2009               [Page 51]

Internet-Draft                   XMPP IM                       July 2008


5.  Exchanging Messages

   Once a client has authenticated with a server and bound a resource to
   an XML stream as described in [XMPP-CORE], an XMPP server will route
   XML stanzas to and from that client client.  One kind of stanza that can be
   exchanged is <message/> (if, that is, messaging functionality is
   enabled and the server is not a presence-only service).  One kind of stanza that may be exchanged is <message/>.  Exchanging
   messages is a basic use of XMPP and occurs when a user generates a
   message stanza that is addressed to another entity.  As defined under Server Rules for Processing XML Stanzas (Section 8),
   Section 8, the sender's server is responsible for delivering the
   message to the intended recipient (if the recipient is on the same
   local server) or for routing the message to the recipient's server
   (if the recipient is on a different remote server).  Thus a message stanza is
   used to "push" information to another entity.

   As noted under Section 4.6, if a user exchanges messages with another
   entity but does not share presence with the entity based on a
   presence subscription, it is RECOMMENDED for the user's client to
   send directed presence to the other entity.

   The following sections describe the syntax of the <message/> stanza.

5.1.  Attributes

5.1.1.  To Attribute

   An  One-to-One Chat Sessions

   In practice, instant messaging client SHOULD specify an intended recipient for
   a message by providing the JID activity between human users tends to
   occur in form of an entity other than a conversational burst that we call a CHAT SESSION:
   the sender exchange of at least several messages between two parties in
   the 'to' attribute
   relatively rapid succession within a relatively brief period of the <message/> stanza.

   If the time.

   When a human user intends to engage in such a chat session with a
   contact (rather than sending a single message to which no reply is being sent outside
   expected), the context user's client SHOULD send a message of any existing chat
   session or received message, type "chat" and
   the value of contact's client SHOULD preserve that message type in subsequent
   replies.  The user's client also SHOULD include a <thread/> element
   with its initial message, which the 'to' address contact's client SHOULD be
   of also
   preserve during the form <user@domain> rather than life of the form
   <user@domain/resource>.





Saint-Andre             Expires December 8, 2008               [Page 45]

Internet-Draft                   XMPP IM                       June 2008


   <message
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <body>Art thou not Romeo, and a Montague?</body>
   </message>

   If chat session.

   The user's client MUST address the initial message is being sent in reply to a message previously
   received from an address of chat session
   to the form <user@domain/resource> (e.g.,
   within bare JID <contact@domain> (rather than attempting to guess an
   appropriate full JID <contact@domain/resource>).  Until and unless
   the context of user's client receives a chat session), reply from the value of contact, it MUST continue
   sending any further messages to the 'to' address contact's bare JID.  The
   contact's client SHOULD be of address its subsequent replies to the form user's
   full JID <user@domain/resource> rather than of as provided in the form
   <user@domain> unless 'from' address of
   the sender has knowledge (via presence) that initial message.  Once the
   intended recipient's resource user's client receives a reply from
   the contact's full JID, it SHOULD address its subsequent messages to
   the contact's full JID as provided in the 'from' address of the
   contact's replies.

   As noted under Section 4.6, if a user exchanges message stanzas with
   another entity but does not share presence with the entity based on a
   presence subscription, it is RECOMMENDED for the user's client to
   send directed presence to the other entity.

   An example of a chat session is provided under Section 7.



Saint-Andre             Expires January 13, 2009               [Page 52]

Internet-Draft                   XMPP IM                       July 2008


5.2.  Message Syntax

   The following sections describe the syntax of the <message/> stanza.

5.2.1.  To Attribute

   An instant messaging client specifies an intended recipient for a
   message by providing the JID of an entity other than the sender in
   the 'to' attribute of the <message/> stanza.

   If the message is being sent outside the context of any existing chat
   session or received message, the value of the 'to' address SHOULD be
   of the form <user@domain> rather than of the form
   <user@domain/resource>.

   <message
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <body>Art thou not Romeo, and a Montague?</body>
   </message>

   If the message is being sent in reply to a message previously
   received from an address of the form <user@domain/resource> (e.g.,
   within the context of a one-to-one chat session as described under
   Section 5.1), the value of the 'to' address SHOULD be of the form
   <user@domain/resource> rather than of the form <user@domain> unless
   the sender has knowledge (via presence) that the intended recipient's
   resource is no longer available.

   <message
       from='romeo@example.net/orchard'
       to='juliet@example.com/balcony'
       type='chat'
       xml:lang='en'>
     <body>Neither, fair saint, if either thee dislike.</body>
   </message>

5.1.2.

5.2.2.  Type Attribute

   Common uses of the message stanza in instant messaging applications
   include
   include: single messages, messages; messages sent in the context of a one-to-
   one chat
   conversation, session; messages sent in the context of a multi-user chat room,
   headlines and other
   room; alerts, notifications, or other information to which no reply
   is expected; and errors.  These uses are differentiated via the
   'type' attribute.  Inclusion of the 'type' attribute is RECOMMENDED.
   If included, the 'type' attribute MUST have one of the following



Saint-Andre             Expires January 13, 2009               [Page 53]

Internet-Draft                   XMPP IM                       July 2008


   values:

   o  chat -- The message is sent in the context of a one-to-one chat
      session.  A receiving client SHOULD present the message in an
      interface enabling one-to-one chat between the two parties,
      including an appropriate conversation history.  Detailed
      recommendations regarding one-to-one chat sessions are provided
      under Section 5.4. 5.1.
   o  error -- The message is generated by an entity that experiences an
      error in processing a message received from another entity (for
      details regarding stanza error syntax, refer to [XMPP-CORE]).  A
      client that receives a message of type "error" SHOULD present an
      appropriate interface informing the sender of the nature of the
      error.
   o  groupchat -- The message is sent in the context of a multi-user
      chat environment (similar to that of [IRC]).  A receiving client
      SHOULD present the message in an interface enabling many-to-many



Saint-Andre             Expires December 8, 2008               [Page 46]

Internet-Draft                   XMPP IM                       June 2008
      chat between the parties, including a roster of parties in the
      chatroom and an appropriate conversation history.  Full definition  Definition of
      XMPP-based groupchat protocols functionality is out of scope for this
      document (for details, refer to [XEP-0045]).
   o  headline -- The message is probably generated by provides an automated
      service that delivers alert, a notification, or broadcasts content (news, sports,
      other information to which no reply is expected (e.g., news
      headlines, sports updates, near-real-time market
      information, data, and
      syndicated content, alerts, etc.), or the sender
      wishes the message to be delivered as if it were so generated.  No content).  Because no reply to the message is expected,
      and a receiving client SHOULD present the message in an interface
      that appropriately differentiates the message from standalone
      messages, chat
      sessions, messages, or groupchat sessions messages (e.g., by not
      providing the recipient with the ability to reply).  The receiving
      server SHOULD deliver the message to all of the recipient's
      available resources.
   o  normal -- The message is a standalone message that is sent outside
      the context of a one-to-one conversation or groupchat, and to
      which it is expected that the recipient will reply.  A receiving
      client SHOULD present the message in an interface enabling the
      recipient to reply, but without a conversation history.  This is
      the default value of the 'type' attribute.

   An IM application SHOULD support all of the foregoing message types.
   If an application receives a message with no 'type' attribute or the
   application does not understand the value of the 'type' attribute
   provided, it MUST consider the message to be of type "normal" (i.e.,
   "normal" is the default).

   Although the 'type' attribute is OPTIONAL, it is considered polite to
   mirror the type in any replies to a message; furthermore, some
   specialized applications (e.g., a multi-user chat service) MAY at
   their discretion enforce the use of a particular message type (e.g.,
   type='groupchat').

5.2.  Child Elements

   An XMPP message stanza MAY contain any allowable child elements
   qualified by the 'jabber:client' (or 'jabber:server') namespace, as
   well as any other properly-namespaced child element that consists of
   extended content.  The defined payloads are described in the
   following sections and extended content payloads are described in the
   appropriate



Saint-Andre             Expires January 13, 2009               [Page 54]

Internet-Draft                   XMPP extension specifications (not herein).

5.2.1. IM                       July 2008


   type='groupchat').

5.2.3.  Body Element

   The <body/> element contains human-readable XML character data that
   specifies the textual contents of the message; this child element is
   normally included but is OPTIONAL.




Saint-Andre             Expires December 8, 2008               [Page 47]

Internet-Draft                   XMPP IM                       June 2008

   <message
       to='romeo@example.net'
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <body>Wherefore art thou, Romeo?</body>
   </message>

   The <body/> element MUST NOT possess any attributes, with the
   exception of the 'xml:lang' attribute.  Multiple instances of the
   <body/> element MAY be included in a message stanza, but only if each
   instance possesses an 'xml:lang' attribute with a distinct language
   value (either explicitly or by inheritance from the 'xml:lang' value
   of an element farther up in the XML hierarchy, which may can include the
   XML stream header as described in [XMPP-CORE]).

   <message
       to='romeo@example.net'
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <body>Wherefore art thou, Romeo?</body>
     <body xml:lang='cs'>
        Pro&#x010D;e&#x017D; jsi ty, Romeo?
      </body>
   </message>

   The <body/> element MUST NOT contain mixed content (as defined in
   Section 3.2.2 of [XML]).

5.2.2.

5.2.4.  Subject Element

   The <subject/> element contains human-readable XML character data
   that specifies the topic of the message.









Saint-Andre             Expires January 13, 2009               [Page 55]

Internet-Draft                   XMPP IM                       July 2008


   <message
       to='romeo@example.net'
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <subject>I implore you!</subject>
     <body>Wherefore art thou, Romeo?</body>
   </message>

   The <subject/> element MUST NOT possess any attributes, with the
   exception of the 'xml:lang' attribute.  Multiple instances of the
   <subject/> element MAY be included for the purpose of providing
   alternate versions of the same subject, but only if each instance



Saint-Andre             Expires December 8, 2008               [Page 48]

Internet-Draft                   XMPP IM                       June 2008
   possesses an 'xml:lang' attribute with a distinct language value
   (either explicitly or by inheritance from the 'xml:lang' value of an
   element farther up in the XML hierarchy, which may can include the XML
   stream header as described in [XMPP-CORE]).

   <message
       to='romeo@example.net'
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <subject>I implore you!</subject>
     <subject xml:lang='cs'>
       &#x00DA;p&#x011B;nliv&#x011B; pros&#x00EDm!
     </subject>
     <body>Wherefore art thou, Romeo?</body>
     <body xml:lang='cs'>
        Pro&#x010D;e&#x017E; jsi ty, Romeo?
      </body>
   </message>

   The <subject/> element MUST NOT contain mixed content (as defined in
   Section 3.2.2 of [XML]).

5.2.3.

5.2.5.  Thread Element

   The primary use of the XMPP <thread/> element is to uniquely identify
   a conversation thread or "chat session" between two entities
   instantiated by <message/> stanzas of type 'chat'.  However, the XMPP
   <thread/> element may can also be used to uniquely identify an analogous
   thread between two entities instantiated by <message/> stanzas of
   type 'headline' or 'normal', or among multiple entities in the
   context of a multi-user chat room instantiated by <message/> stanzas
   of type 'groupchat'.  It may MAY also be used for <message/> stanzas not
   related to a human conversation, such as a game session or an
   interaction between plugins.  The <thread/> element is not used to



Saint-Andre             Expires January 13, 2009               [Page 56]

Internet-Draft                   XMPP IM                       July 2008


   identify individual messages, only conversations. conversations or messagingg
   sessions.

   The inclusion of the <thread/> element is OPTIONAL.  Because the
   <thread/> element uniquely identifies the particular conversation
   thread to which a message belongs, a message stanza MUST NOT contain
   more than one <thread/> element.

   The value of the <thread/> element is not human-readable and MUST be
   treated as opaque by entities; no semantic meaning may can be derived
   from it, and only exact comparisons may can be made against it.  The
   value of the <thread/> element MUST be a universally unique
   identifier (UUID) as described in [UUID].




Saint-Andre             Expires December 8, 2008               [Page 49]

Internet-Draft                   XMPP IM                       June 2008

   The <thread/> element MAY possess a 'parent' attribute that
   identifies another thread of which the current thread is an offshoot
   or child; the value of the 'parent' MUST conform to the syntax of the
   <thread/> element itself.  The <thread/> element MUST NOT contain
   mixed content (as defined in Section 3.2.2 of [XML]).

   <message
       to='romeo@example.net'
       from='juliet@example.com/balcony'
       type='chat'
       xml:lang='en'>
     <subject>I implore you!</subject>
     <subject xml:lang='cs'>
       &#x00DA;p&#x011B;nliv&#x011B; pros&#x00EDm!
     </subject>
     <body>Wherefore art thou, Romeo?</body>
     <body xml:lang='cs'>
        Pro&#x010D;e&#x017E; jsi ty, Romeo?
     </body>
     <thread parent='e0ffe42b28561960c6b12b944a092794b9683a38'>
       0e3141cd80894871a68e6fe6b1ec56fa
     </thread>
   </message>

   For detailed recommendations regarding use of the <thread/> element,
   refer to [XEP-0201].

5.3.  Extended Content

   As described in [XMPP-CORE], an XML stanza MAY contain any properly-
   namespaced child element; this applies to the message stanza as well.

   (In the following example, the message stanza includes an XHTML-
   formatted version of the message as defined in [XEP-0071]).)

   <message
       to='romeo@example.net'
       from='juliet@example.com/balcony'
       type='chat'
       xml:lang='en'>
     <body>Wherefore art thou, Romeo?</body>
     <html xmlns='http://jabber.org/protocol/xhtml-im'>
       <body xmlns='http://www.w3.org/1999/xhtml'>
         Wherefore <span style='font-style: italic'>art</span>
         thou, <span style='color:red'>Romeo</span>?
       </body>
     </html>
   </message>



Saint-Andre             Expires December 8, 2008               [Page 50]

Internet-Draft                   XMPP IM                       June 2008


5.4.  One-to-One Chat Sessions

   In practice, instant messaging activity between human users tends to
   occur in form of a conversational burst that we call a CHAT SESSION:
   the exchange of at least several messages between two parties in
   relatively rapid succession within a relatively brief period of time.

   When a human user intends to engage in such a chat session with a
   contact (rather than sending a single message to which no reply is
   expected), the user's client SHOULD send a message of type "chat" and
   the contact's client SHOULD preserve that message type in subsequent
   replies.  The user's client also SHOULD include a <thread/> element
   on its initial message, which the contact's client SHOULD also
   preserve during the life of the chat session.

   The user's client MUST address the initial message in a chat session
   to the bare JID <contact@domain> (rather than attempting to guess an
   appropriate full JID <contact@domain/resource>).  Until and unless
   the user's client receives a reply from the contact, it MUST continue
   sending any further messages to the contact's bare JID.  The
   contact's client SHOULD address its subsequent replies to the user's
   full JID <user@domain/resource> as provided in the 'from' address of
   the initial message.  Once the user's client receives a reply from
   the contact's full JID, it SHOULD address its subsequent messages to
   the contact's full JID as provided in the 'from' address value of the
   contact's replies.

   If a user exchanges messages with a contact but the user does not
   normally share presence with 'parent' MUST conform to the contact via a presence subscription,
   it is RECOMMENDED for syntax of the user's client to send directed presence to
   <thread/> element itself.

   The <thread/> element MUST NOT contain mixed content (as defined in
   Section 3.2.2 of [XML]).

   <message
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <subject>I implore you!</subject>
     <subject xml:lang='cs'>
       &#x00DA;p&#x011B;nliv&#x011B; pros&#x00EDm!
     </subject>
     <body>Wherefore art thou, Romeo?</body>
     <body xml:lang='cs'>
        Pro&#x010D;e&#x017E; jsi ty, Romeo?
     </body>
     <thread parent='e0ffe42b28561960c6b12b944a092794b9683a38'>
       0e3141cd80894871a68e6fe6b1ec56fa
     </thread>
   </message>

   For detailed recommendations regarding use of the contact, subject <thread/> element,
   refer to user approval (either explicitly for this
   contact or implicitly via a configuration setting).  If [XEP-0201].

5.3.  Extended Content

   As described in [XMPP-CORE], an XML stanza MAY contain any child
   element that is qualified by a client
   supports this feature, it MUST allow namespace other than the user default
   namespace; this applies to disable the feature
   in order to prevent presence sharing with unknown entities.

   An example message stanza as well.



Saint-Andre             Expires January 13, 2009               [Page 57]

Internet-Draft                   XMPP IM                       July 2008


   (In the following example, the message stanza includes an XHTML-
   formatted version of a chat session the message as described above is provided under
   Section 7. defined in [XEP-0071]).)

   <message
       from='juliet@example.com/balcony'
       to='romeo@example.net'
       type='chat'
       xml:lang='en'>
     <body>Wherefore art thou, Romeo?</body>
     <html xmlns='http://jabber.org/protocol/xhtml-im'>
       <body xmlns='http://www.w3.org/1999/xhtml'>
         Wherefore <span style='font-style: italic'>art</span>
         thou, <span style='color:red'>Romeo</span>?
       </body>
     </html>
   </message>


6.  Exchanging IQ Stanzas

   As described in [XMPP-CORE], IQ stanzas provide a structured request-
   response mechanism.  The basic semantics of that mechanism (e.g.,
   that the 'id' attribute is required) mandatory) are defined in [XMPP-CORE],
   whereas the specific semantics required needed to complete particular use
   cases are defined in all cases instances by the extended namespace that
   qualifies the direct child element of an IQ stanza of type "get" or
   "set".  The 'jabber:client' and 'jabber:server' namespaces do not



Saint-Andre             Expires December 8, 2008               [Page 51]

Internet-Draft                   XMPP IM                       June 2008
   define any children of IQ stanzas other than the <error/> element
   common to all stanza types.  This document defines one such extended
   namespace, for Managing the Roster (Section 2).  However, an IQ
   stanza MAY contain structured information qualified by any extended
   namespace.

   As noted under Section 4.6, if a user exchanges IQ stanzas with
   another entity but does not share presence with the entity based on a
   presence subscription, it is RECOMMENDED for the user's client to
   send directed presence to the other entity.


7.  A Sample Session

   The examples in this section illustrate a possible instant messaging
   and presence session.  The user is romeo@example.net, he has an
   available resource whose resource identifier is "orchard", and he has
   the following individuals in his roster:






Saint-Andre             Expires January 13, 2009               [Page 58]

Internet-Draft                   XMPP IM                       July 2008


   o  juliet@example.com (subscription="both" and she has two available
      resources, one whose resource identifier is "chamber" and another
      whose resource identifier is "balcony")
   o  benvolio@example.org  benvolio@example.net (subscription="to")
   o  mercutio@example.org (subscription="from")

   First, the user completes the preconditions (stream establishment,
   TLS and SASL negotiation, and resource binding) described in
   [XMPP-CORE]; those protocol flows are not reproduced here.

   Next, the user requests his roster.

   Example 1: User requests current roster from server:

   UC: <iq from='romeo@example.net/balcony' type='get' id='ex1'>
           id='ex1'
           type='get'>
         <query xmlns='jabber:iq:roster'/>
       </iq>
















Saint-Andre             Expires December 8, 2008               [Page 52]

Internet-Draft                   XMPP IM                       June 2008

   Example 2: User receives roster from server:

   US: <iq to='romeo@example.net/balcony' type='result' id='ex1'>
           id='ex1'
           type='result'>
         <query xmlns='jabber:iq:roster'>
           <item jid='romeo@example.com'
                 name='Juliet'
                 subscription='both'>
             <group>Friends</group>
           </item>
           <item jid='benvolio@example.org'
                 name='Benvolio'
                 subscription='to'/>
           <item jid='mercutio@example.org'
                 name='Mercutio'
                 subscription='from'/>
         </query>
       </iq>

   Now the user begins a presence session.

   Example 3: User sends initial presence:

   UC: <presence from='romeo@example.net/orchard'/>






Saint-Andre             Expires January 13, 2009               [Page 59]

Internet-Draft                   XMPP IM                       July 2008


   Example 4: User's server sends presence probes to contacts with
   subscription="to" and subscription="both" on behalf of the user's
   available resource:

   US: <presence
           type='probe'
           from='romeo@example.net/orchard'
           to='juliet@example.com'/>
           to='juliet@example.com'
           type='probe'/>

   US: <presence
           type='probe'
           from='romeo@example.net/orchard'
           to='benvolio@example.org'/>
           to='benvolio@example.org'
           type='probe'/>

   Example 5: User's server sends initial presence to contacts with
   subscription="from" and subscription="both" on behalf of the user's
   available resource:

   US: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'/>

   US: <presence
           from='romeo@example.net/orchard'
           to='mercutio@example.org'/>


























Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 53] 60]

Internet-Draft                   XMPP IM                       June                       July 2008


           to='mercutio@example.org'/>


   Example 6: Contacts' servers reply to presence probe on behalf of all
   available resources:

   CS: <presence
           from='juliet@example.com/balcony'
           to='romeo@example.net/orchard'
           xml:lang='en'>
         <show>away</show>
         <status>be right back</status>
         <priority>0</priority>
       </presence>

   CS: <presence
           from='juliet@example.com/chamber'
           to='romeo@example.net/orchard'>
         <priority>1</priority>
       </presence>

   CS: <presence
           from='benvolio@example.org/pda'
           to='romeo@example.net/orchard'
           xml:lang='en'>
         <show>dnd</show>
         <status>gallivanting</status>
       </presence>

   Example 7: Contacts' servers deliver user's initial presence to all
   available resources or return unsubscribed to user: resources:

   CS: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'/>

   CS: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'/>

   CS: <presence
           from='mercutio@example.org'
           to='romeo@example.net'
           type='unsubscribed'/>
           to='romeo@example.net'/>











Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 54] 61]

Internet-Draft                   XMPP IM                       June                       July 2008


   Example 8: User sends directed presence to another user not in his
   roster:

   UC: <presence
           from='romeo@example.net/orchard'
           to='nurse@example.com'
           xml:lang='en'>
         <show>dnd</show>
         <status>courting Juliet</status>
         <priority>0</priority>
       </presence>

   Now the user has engages in a chat session with one of his contacts.






































Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 55] 62]

Internet-Draft                   XMPP IM                       June                       July 2008


   Example 9: A threaded conversation

   CC: <message
           from='juliet@example.com/balcony'
           to='romeo@example.net'
           type='chat'
           xml:lang='en'>
         <body>My ears have not yet drunk a hundred words</body>
         <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
       </message>

   CC: <message
           from='juliet@example.com/balcony'
           to='romeo@example.net'
           type='chat'
           xml:lang='en'>
         <body>Of that tongue's utterance, yet I know the sound:</body>
         <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
       </message>

   CC: <message
           from='juliet@example.com/balcony'
           to='romeo@example.net'
           type='chat'
           xml:lang='en'>
         <body>Art thou not Romeo, and a Montague?</body>
         <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
       </message>

   UC: <message
           from='romeo@example.net/orchard'
           to='juliet@example.com/balcony'
           type='chat'
           xml:lang='en'>
         <body>Neither, fair saint, if either thee dislike.</body>
         <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
       </message>

   CC: <message
           from='juliet@example.com/balcony'
           to='romeo@example.net/orchard'
           type='chat'
           xml:lang='en'>
         <body>How cam'st thou hither, tell me, and wherefore?</body>
         <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
       </message>

   And so on.



Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 56] 63]

Internet-Draft                   XMPP IM                       June                       July 2008


   The user can also send subsequent broadcasted presence. presence broadcast.

   Example 10: User sends updated available presence for broadcasting:

   UC: <presence xml:lang='en'>
         <show>away</show>
         <status>I shall return!</status>
         <priority>1</priority>
       </presence>

   Example 11: User's server broadcasts updated presence only to one
   contact:

   US: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'
           xml:lang='en'>
         <show>away</show>
         <status>I shall return!</status>
         <priority>1</priority>
       </presence>

   Example 12: Contact's server delivers updated presence to all of the
   contact's available resources ("balcony" and "chamber"):

   CS: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'
           xml:lang='en'>
         <show>away</show>
         <status>I shall return!</status>
         <priority>1</priority>
       </presence>

   CS: <presence
           from='romeo@example.net/orchard'
           to='juliet@example.com'
           xml:lang='en'>
         <show>away</show>
         <status>I shall return!</status>
         <priority>1</priority>
       </presence>

   Example 13: One of the contact's resources broadcasts unavailable
   presence:

   CC: <presence from='juliet@example.com/chamber' type='unavailable'/>




Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 57] 64]

Internet-Draft                   XMPP IM                       June                       July 2008


   Example 14: Contact's server sends unavailable presence to user:

   CS: <presence
           type='unavailable'
           from='juliet@example.com/chamber'
           to='romeo@example.net'/>
           to='romeo@example.net'
           type='unavailable'/>

   Now the user ends his presence session.

   Example 15: User sends unavailable presence:

   UC: <presence from='romeo@example.net/orchard'
                 type='unavailable'
                 xml:lang='en'>
         <status>gone home</status>
       </presence>

   Example 16: User's server broadcasts unavailable presence to contact contacts
   as well as to the person to whom the user sent directed presence:

   US: <presence
           type='unavailable'
           from='romeo@example.net/orchard'
           to='juliet@example.com'
           type='unavailable'
           xml:lang='en'>
         <status>gone home</status>
       </presence>

   US: <presence
           type='unavailable'
           from='romeo@example.net/orchard'
           to='nurse@example.com'
           type='unavailable'
           xml:lang='en'>
         <status>gone home</status>
       </presence>

   Finally the user closes his stream and the server responds in kind.

   Example 17: User closes stream:

   UC: </stream:stream>

   Example 18: User's server closes stream:

   US: </stream:stream>

   THE END




Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 58] 65]

Internet-Draft                   XMPP IM                       June                       July 2008


8.  Server Rules for Processing XML Stanzas

   Basic server rules for processing XML stanzas are defined in
   [XMPP-CORE].  This section defines supplementary rules for XMPP
   instant messaging and presence servers; in the absence of a
   supplementary rule defined below (e.g., for stanzas without a 'to'
   address), the rule defined in [XMPP-CORE] shall apply. applies.

8.1.  No Such User

   If the user account identified by the 'to' attribute does not exist,
   how the stanza shall be is processed depends on the stanza type.

   o  For an IQ stanza, the server MUST return a <service-unavailable/>
      stanza error to the sender.
   o  For a message stanza, the server SHOULD MUST return a <service-
      unavailable/> stanza error to the sender.
   o  For a presence stanza with no 'type' attribute or a 'type'
      attribute of "unavailable", the server SHOULD MUST silently ignore the
      stanza.
   o  For a presence stanza (i.e., not of type "subscribe", the server MUST return an error or
      a presence stanza of type
      "unsubscribed"). "unsubscribed".
   o  For a presence stanza of type "subscribe", "subscribed", "unsubscribe", or
      "unsubscribed", the server MUST follow silently ignroe the
      guidelines provided under Section 3. stanza.

8.2.  Full JID at Local Domain

   If the hostname of the domain identifier portion of the JID contained
   in the 'to' attribute of an inbound stanza matches one of the
   configured hostnames of the server itself and the JID contained in
   the 'to' attribute is of the form <user@domain/resource>, the server
   MUST adhere to the following rules.

8.2.1.  Available Resource Matches

   If an available resource exactly matches the full JID, how the
   recipient's server MUST deliver stanza
   is processed depends on the stanza to that resource (subject
   to appropriate security policies as described under Section 11 and in
   [XMPP-CORE]).

   However, for type.

   o  For an IQ stanzas of type "get" or "set", if the intended
      recipient does not share presence with the requesting entity
      either by means of a presence subscription of type "both" or
      "from" or by means of directed presence, then the server SHOULD
      NOT deliver the IQ stanza but instead SHOULD return a <service-unavailable/> <service-
      unavailable/> stanza error to the requesting entity.  This policy
      helps to prevent presence leaks (see Section 11).
   o  For a message stanza, the server MUST deliver the stanza to the
      resource.




Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 59] 66]

Internet-Draft                   XMPP IM                       June                       July 2008


   o  For a presence stanza with no 'type' attribute or a 'type'
      attribute of "unavailable", the server MUST deliver the stanza to
      the resource.
   o  For a presence stanza of type "subscribe", the server MUST follow
      the guidelines provided under Section 3.1.3.
   o  For a presence stanza of type "subscribe", "subscribed",
      "unsubscribe", or "unsubscribed", the server MUST follow the
      guidelines provided under Section 3.

8.2.2.  No Available Resource Matches

   If no connected or available resource exactly matches the full JID,
   how the stanza shall be is processed depends on the stanza type. type.

   o  For an IQ stanza, the server MUST return a <service-unavailable/>
      stanza error to the sender.
   o  For a message, message stanza, the server SHOULD treat the stanza as if it
      were addressed to <user@domain> as described in the next section.
   o  For a presence stanza with no 'type' attribute or a 'type'
      attribute of "unavailable", the server SHOULD MUST silently ignore the
      stanza (i.e., not return an error or a presence stanza of type
      "unsubscribed").
      stanza.
   o  For a presence stanza of type "subscribe", "subscribed",
      "unsubscribe", or "unsubscribed", the server MUST follow
      the guidelines provided under Section 3. 3.1.3.
   o  For an IQ stanza, a presence stanza of type "subscribed", "unsubscribe", or
      "unsubscribed", the server MUST return a <service-unavailable/>
      stanza error to ignore the sender. stanza.

8.3.  Bare JID at Local Domain

   If the hostname of the domain identifier portion of the JID contained
   in the 'to' attribute of an inbound stanza matches one of the
   configured hostnames of the server itself and the JID contained in
   the 'to' attribute is of the form <user@domain>, the server MUST
   adhere to the following rules.

8.3.1.  Available Resources

   If there is at least one available resource, how the stanza shall be is
   processed depends on the stanza type.

8.3.1.1.  Message

   For a message stanza of type "headline", the server SHOULD deliver
   the stanza to all available resources.

   For a message stanza of type "chat", "error", "groupchat", or
   "normal", the server SHOULD deliver the stanza to the highest-
   priority available resource.  If there is not one highest-priority
   available resource but instead the highest priority is asserted by



Saint-Andre             Expires January 13, 2009               [Page 67]

Internet-Draft                   XMPP IM                       July 2008


   two or more available resources, these resources are said to form a
   "delivery tie".  In the case of a delivery tie, a server SHOULD
   deliver the message to all of the tied resources.  However, before
   delivering the message, a server MAY remove one or more resources
   from the tie.  Methods for doing so are outside the scope of this
   specification, but could include factors such as the resource's time
   of connection, time of last network or application activity,
   availability as determined by some hierarchy of <show/> values, or
   user-configured rules.  Nevertheless, a server MUST NOT remove all



Saint-Andre             Expires December 8, 2008               [Page 60]

Internet-Draft                   XMPP IM                       June 2008
   resources from the tie, and MUST deliver the message to at least one
   of the highest-priority resources (subject to appropriate security
   policies as described under Section 11 and in [XMPP-CORE]).

   However, for any message type the server MUST NOT deliver the stanza
   to any available resource with a negative priority; if the only
   available resource has a negative priority, the server SHOULD handle
   the message as if there were no available resources as described
   under Section 8.3.2.

   In all cases, the server MUST NOT rewrite the 'to' attribute (i.e.,
   it MUST leave it as <user@domain> rather than change it to
   <user@domain/resource>).

8.3.1.2.  Presence

   For a presence stanza of type "probe", the server MUST handle it
   directly as described under Section 4.3.

   For a presence stanza with no type or of type "unavailable", the
   server MUST deliver the stanza to all available resources.

   For a presence stanza of type "subscribe", "subscribed",
   "unsubscribe", or "unsubscribed", the server MUST adhere to the rules
   defined under Section 3 and summarized under Appendix A.

   In all cases, the server MUST NOT rewrite the 'to' attribute (i.e.,
   it MUST leave it as <user@domain> rather than change it to
   <user@domain/resource>).

8.3.1.3.  IQ

   For an IQ stanza, the server itself MUST reply on behalf of the user
   with either an IQ result or an IQ error, and MUST NOT deliver the IQ
   stanza to any of the user's available resources.  Specifically, if
   the semantics of the qualifying namespace define a reply that the
   server can provide on behalf of the user, the server MUST reply to
   the stanza on behalf of the user by returning either an IQ stanza of
   type "result" or an IQ stanza of type "error" that is appropriate to



Saint-Andre             Expires January 13, 2009               [Page 68]

Internet-Draft                   XMPP IM                       July 2008


   the original payload; if not, the server MUST reply with a <service-
   unavailable/> stanza error.

8.3.2.  No Available Resources

   If there are no available resources associated with the user, how the
   stanza shall be is processed depends on the stanza type.





Saint-Andre             Expires December 8, 2008               [Page 61]

Internet-Draft                   XMPP IM                       June 2008

8.3.2.1.  Message

   In order to properly handle message stanzas, it is strongly
   RECOMMENDED for an implementation to support , OFFLIST STORAGE, i.e.,
   the server SHOULD store the stanza on behalf of the user and deliver
   it when the user next becomes available.  For recommendations
   regarding offline message storage refer to [XEP-0160].

   For a message stanza of type "chat", "groupchat", or "normal", the
   server SHOULD add the message to offline storage or forward the
   message to the user via a non-XMPP messaging system (e.g., to the
   user's email account).  However, if offline message storage or
   message forwarding is not enabled, the server SHOULD MUST return a
   <service-unavailable/> <service-
   unavailable/> stanza error to the sender.

   For a message stanza of type "headline", the server SHOULD NOT added add
   the message to offline storage but instead SHOULD silently discard
   the message (i.e., neither deliver it to the intended recipient nor
   return an error to the sender).

   For a message stanza of type "error", the server MUST NOT added add the
   message to offline storage but instead SHOULD silently discard the
   message (i.e., neither deliver it to the intended recipient nor
   return an error to the sender).

8.3.2.2.  Presence

   For a presence stanza with no type or of type "unavailable" or
   "probe", the server SHOULD silently ignore the stanza by not storing
   it for later delivery and not replying to it on behalf of the user.

   For a presence stanza of type "subscribe", "subscribed",
   "unsubscribe", or "unsubscribed", the server MUST adhere to the rules
   defined under Section 3 and summarized under Appendix A.

8.3.2.3.  IQ

   For an IQ stanza, the server itself MUST reply on behalf of the user
   with either an IQ result or an IQ error.  Specifically, if the
   semantics of the qualifying namespace define a reply that the server



Saint-Andre             Expires January 13, 2009               [Page 69]

Internet-Draft                   XMPP IM                       July 2008


   can provide on behalf of the user, the server MUST reply to the
   stanza on behalf of the user by returning either an IQ stanza of type
   "result" or an IQ stanza of type "error" that is appropriate to the
   original payload; if not, the server MUST reply with a <service-
   unavailable/> stanza error.






Saint-Andre             Expires December 8, 2008               [Page 62]

Internet-Draft                   XMPP IM                       June 2008

8.4.  Foreign  Remote Domain

   If the hostname of the domain identifier portion of the address
   contained in the 'to' attribute of an outbound stanza does not match
   a configured hostname of the server itself, the server MUST attempt
   to route the stanza to the foreign remote domain.  If there exists an active
   stream between the two peers, the server shall MUST route the stanza over
   that stream for processing by the peer server.  If not, the server
   MUST do the following.

   First, resolve the hostname of the foreign remote domain (or use a cached
   resolution of the foreign remote domain to an IP address).  The recommended RECOMMENDED
   order of attempted resolutions is as follows:

   1.  Attempt to resolve the foreign remote hostname using a DNS service
       location record [SRV] Service of "xmpp-server" and a Proto of
       "tcp", resulting in resource records such as "_xmpp-
       server._tcp.example.com.", as specified in [XMPP-CORE].
   2.  If the "xmpp-server" address record resolution fails, attempt to
       resolve the "_im" or "_pres" SRV Service as specified in
       [IMP-SRV], using the "_im" Service for <message/> stanzas and the
       "_pres" Service for <presence/> stanzas (it is up to the
       implementation how to handle <iq/> stanzas).  This will result in
       one or more resolutions of the form "_im.<proto>.example.com." or
       "_pres.<proto>.example.com.", where "<proto>" would be a label
       registered in the Instant Messaging SRV Protocol Label registry
       or the Presence SRV Protocol Label registry: either "_xmpp" for
       an XMPP-aware domain or some other IANA-registered label (e.g.,
       "_simple") for a non-XMPP-aware domain.
   3.  If both SRV address record resolutions fail, attempt to perform a
       normal IPv4/IPv6 address record resolution to determine the IP
       address using the "xmpp-server" port of 5269 registered with the
       IANA, as specified in [XMPP-CORE].

   If the server cannot resolve the foreign remote domain, it SHOULD MUST return a
   <remote-server-not-found/> stanza error.

   Second, negotiate XML streams with the foreign remote domain by following the
   process defined in [XMPP-CORE].  If the server can resolve the
   foreign remote
   domain but cannot establish streams with the XMPP service at that
   domain, it SHOULD MUST return a <remote-server-timeout/> stanza error.




Saint-Andre             Expires January 13, 2009               [Page 70]

Internet-Draft                   XMPP IM                       July 2008


   Third, route the stanza to the foreign remote domain for processing by the
   peer server.

   Note: Administrators of server deployments are strongly encouraged to
   keep the _im._xmpp, _pres._xmpp, and _xmpp._tcp SRV records properly



Saint-Andre             Expires December 8, 2008               [Page 63]

Internet-Draft                   XMPP IM                       June 2008
   synchronized, since different implementations might perform the "_im"
   and "_pres" lookups before the "xmpp-server" lookup.


9.  IM and Presence Compliance Requirements

   This section summarizes the specific aspects of the Extensible
   Messaging and Presence Protocol that MUST be supported by instant
   messaging and presence servers and clients in order to be considered
   compliant implementations.  All such applications MUST comply with
   the requirements specified in [XMPP-CORE].  The text in this section
   specifies additional compliance requirements for instant messaging
   and presence servers and clients (the requirements described here
   supplement but do not supersede the core requirements).

   Note: A server or client MAY support only presence or instant
   messaging, and
   messaging; therefore is not required necessary to support both if only a
   presence service or an instant messaging service is desired.

9.1.  Servers

   In addition to the core server compliance requirements, an instant
   messaging and presence server MUST additionally support all server-
   related instant messaging and presence syntax and semantics defined
   in this document, including:

   o  Presence broadcast on behalf of clients as specified under
      Section 4
   o  Presence subscriptions as specified under Section 3
   o  Roster storage and management as specified under Section 2
   o  IM-specific routing and delivery rules as specified under
      Section 8

9.2.  Clients

   In addition to the core client compliance requirements, an instant
   messaging and presence client MUST additionally support the following
   protocols:

   o  Generation and processing of the IM-specific semantics of XML
      stanzas as defined by the XML schemas, including the 'type'
      attribute of message and presence stanzas as well as their child
      elements (see Section 5 and Section 4)



Saint-Andre             Expires January 13, 2009               [Page 71]

Internet-Draft                   XMPP IM                       July 2008


   o  All client-related instant messaging syntax and semantics defined
      in this document, including presence subscriptions and roster
      management (see Section 3 and Section 2)





Saint-Andre             Expires December 8, 2008               [Page 64]

Internet-Draft                   XMPP IM                       June 2008


   o  End-to-end object signing and encryption as defined in [XMPP-E2E]

   A client MUST also handle addresses that are encoded as "im:" URIs as
   specified in [CPIM] and "pres:" URIs as specified in [CPP], although
   it MAY do so by removing the "im:" or "pres:" scheme and entrusting
   address resolution to the server as specified under Section 8.4.  A
   client SHOULD also handle addresses that are encoded as "xmpp:" URIs
   and IRIs as specified in [XMPP-URI]. [XMPP-URI], although here again it MAY do so
   by removing the scheme and entrusting address resolution to the
   server.


10.  Internationalization Considerations

   For internationalization considerations, refer to the relevant
   section of [XMPP-CORE].


11.  Security Considerations

   Core security considerations for XMPP are defined in the relevant
   section of [XMPP-CORE].

   Additional considerations that apply only to instant messaging and
   presence applications of XMPP are defined in several places within
   this document; specifically:

   o  When a server processes an inbound presence stanza of type "probe"
      whose intended recipient is a user associated with one of the
      server's hostnames, the server MUST NOT reveal the user's presence
      if the sender is an entity that is not authorized to receive that
      information as determined by presence subscriptions (see
      Exchanging Presence Information (Section 4)).
      Section 4).
   o  A user's server MUST NOT leak the user's network availability to
      entities who are not authorized to know the user's presence,
      either via an explicit subscription as described herein or via an
      existing trust relationship (such as presence-enabled user
      directories within organizations).
   o  When a server processes an outbound presence stanza with no type
      or of type "unavailable", it MUST follow the rules defined under
      Exchanging Presence Information (Section 4)
      Section 4 in order to ensure that such presence information is not broadcasted
      sent to entities that are not authorized to know such information.
   o  When a server generates an error stanza in response to receiving a
      stanza for a user who account that does not exist, the use of the <service-
      unavailable/>
      <service-unavailable/> stanza error condition can help protect
      against dictionary attacks, since this is the same error condition



Saint-Andre             Expires January 13, 2009               [Page 72]

Internet-Draft                   XMPP IM                       July 2008


      that is returned if, for instance, the namespace of an IQ child
      element is not understood, or if offline message storage or
      message forwarding is not enabled for a domain.  However, subtle
      differences in the



Saint-Andre             Expires December 8, 2008               [Page 65]

Internet-Draft                   XMPP IM                       June 2008 exact XML of error stanzas, as well as in the
      timing with which such errors are returned, can enable an attacker
      to determine the network presence of a user when more advanced
      blocking technologies are not used (see for instance [XEP-0016]). [XEP-0016]
      and [XEP-0191]).
   o  A client MAY ignore the <status/> element when contained in a
      presence stanza of type "subscribe", "unsubscribe", "subscribed",
      or "unsubscribed" in order to "unsubscribed"; this can help prevent "presence subscription
      spam".


12.  IANA Considerations

   The following sections update the registrations provided in
   [RFC3921].

   For a number of related IANA considerations, refer to the relevant
   section of [XMPP-CORE].

12.1.  Instant Messaging SRV Protocol Label Registration

   Address Resolution for Instant Messaging and Presence [IMP-SRV]
   defines an Instant Messaging SRV Protocol Label registry for
   protocols that can provide services that conform to the "_im" SRV
   Service label.  Because XMPP is one such protocol, the IANA registers
   the "_xmpp" protocol label in the appropriate registry, as follows:

   Protocol label:  _xmpp
   Specification:  XXXX
   Description:  Instant messaging protocol label for the Extensible
      Messaging and Presence Protocol (XMPP) as defined by XXXX.
   Registrant Contact:  IETF, XMPP Working Group, <xmppwg@xmpp.org>

12.2.  Presence SRV Protocol Label Registration

   Address Resolution for Instant Messaging and Presence [IMP-SRV]
   defines a Presence SRV Protocol Label registry for protocols that can
   provide services that conform to the "_pres" SRV Service label.
   Because XMPP is one such protocol, the IANA registers the "_xmpp"
   protocol label in the appropriate registry, as follows:








Saint-Andre             Expires January 13, 2009               [Page 73]

Internet-Draft                   XMPP IM                       July 2008


   Protocol label:  _xmpp
   Specification:  XXXX
   Description:  Presence protocol label for the Extensible Messaging
      and Presence Protocol (XMPP) as defined by XXXX.







Saint-Andre             Expires December 8, 2008               [Page 66]

Internet-Draft                   XMPP IM                       June 2008
   Registrant Contact:  IETF, XMPP Working Group, <xmppwg@xmpp.org>


13.  References

13.1.  Normative References

   [IMP-REQS]
              Day, M., Aggarwal, S., and J. Vincent, "Instant Messaging
              / Presence Protocol Requirements", RFC 2779,
              February 2000.

   [IMP-SRV]  Peterson, J., "Address Resolution for Instant Messaging
              and Presence", RFC 3861, August 2004.

   [SRV]      Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000.

   [TERMS]    Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [UUID]     Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              July 2005.

   [XML]      Paoli, J., Maler, E., Sperberg-McQueen, C., Yergeau, F.,
              and T. Bray, "Extensible Markup Language (XML) 1.0 (Fourth
              Edition)", World Wide Web Consortium Recommendation REC-
              xml-20060816, August 2006,
              <http://www.w3.org/TR/2006/REC-xml-20060816>.

   [XML-NAMES]
              Bray, T., Hollander, D., and A. Layman, "Namespaces in
              XML", W3C REC-xml-names, January 1999,
              <http://www.w3.org/TR/REC-xml-names>.

   [XMPP-CORE]
              Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", draft-saintandre-rfc3920bis-04
              (work in progress), October 2007.

   [XMPP-E2E]

   [XMPP-URI]
              Saint-Andre, P., "End-to-End Signing and Object Encryption
              for the Extensible Messaging and Presence Protocol
              (XMPP)", RFC 3923, October 2004.

   [XMPP-URI] "Internationalized Resource Identifiers



Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 67] 74]

Internet-Draft                   XMPP IM                       June                       July 2008


              Saint-Andre, P., "Internationalized Resource Identifiers


              (IRIs) and Uniform Resource Identifiers (URIs) for the
              Extensible Messaging and Presence Protocol (XMPP)",
              RFC 4622, July 2006.

13.2.  Informative References

   [CPIM]     Peterson, J., "Common Profile for Instant Messaging
              (CPIM)", RFC 3860, August 2004.

   [CPP]      Peterson, J., "Common Profile for Presence (CPP)",
              RFC 3859, August 2004.

   [IMP-MODEL]
              Day, M., Rosenberg, J., and H. Sugano, "A Model for
              Presence and Instant Messaging", RFC 2778, February 2000.

   [IRC]      Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
              April 2000.

   [IRI]      Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [RFC3921]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Instant Messaging and Presence",
              RFC 3921, October 2004.

   [SASL]     Melnikov, A. and K. Zeilenga, "Simple Authentication and
              Security Layer (SASL)", RFC 4422, June 2006.

   [TLS]      Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

   [XEP-0016]
              Millard, P. and P. Saint-Andre, "Privacy Lists", XSF
              XEP 0016, February 2007.

   [XEP-0045]
              Saint-Andre, P., "Multi-User Chat", XSF XEP 0045,
              April 2007.
              January 2008.

   [XEP-0054]
              Saint-Andre, P., "vcard-temp", XSF XEP 0054, March 2003.

   [XEP-0071]
              Saint-Andre, P., "XHTML-IM", XSF XEP 0071, August 2007.

   [XEP-0115]
              Hildebrand, J., Saint-Andre, P., and R. Troncon, "Entity
              Capabilities", XSF XEP 0115, August 2007.



Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 68] 75]

Internet-Draft                   XMPP IM                       June                       July 2008


              Capabilities", XSF XEP 0115, February 2008.

   [XEP-0160]
              Saint-Andre, P., "Best Practices for Handling Offline
              Messages", XSF XEP 0160, January 2006.

   [XEP-0191]
              Saint-Andre, P., "Simple Communications Blocking", XSF
              XEP 0191, February 2007.

   [XEP-0201]
              Saint-Andre, P., Paterson, I., and K. Smith, "Best
              Practices for Message Threads", XSF XEP 0201, August 2007.
              February 2008.

   [XML-SCHEMA]
              Thompson, H., Maloney, M., Mendelsohn, N., and D. Beech,
              "XML Schema Part 1: Structures Second Edition", World Wide
              Web Consortium Recommendation REC-xmlschema-1-20041028,
              October 2004,
              <http://www.w3.org/TR/2004/REC-xmlschema-1-20041028>.

   [VCARD]    Dawson, F. and T. Howes, "vCard MIME Directory Profile",
              RFC 2426, September 1998.


Appendix A.  Subscription States

   This section provides detailed information about subscription states
   and server processing of subscription-related presence stanzas (i.e.,
   presence stanzas of type "subscribe", "subscribed", "unsubscribe",
   and "unsubscribed").

A.1.  Defined States

   There are four primary subscription states (note: these states are
   described from the perspective of the user, not the contact):

   o  None -- the user does not have a subscription to the contact's
      presence, and the contact does not have a subscription to the
      user's presence
   o  To -- the user has a subscription to the contact's presence, but
      the contact does not have a subscription to the user's presence
   o  From -- the contact has a subscription to the user's presence, but
      the user does not have a subscription to the contact's presence
   o  Both -- both the user and the contact have subscriptions to each
      other's presence (i.e., the union of 'from' and 'to')




Saint-Andre             Expires January 13, 2009               [Page 76]

Internet-Draft                   XMPP IM                       July 2008


   These states are supplemented by various pending sub-states to yield
   nine possible subscription states:

   1.  "None" = contact and user are not subscribed to each other, and
       neither has requested a subscription from the other; this is
       reflected in the user's roster by subscription='none'




Saint-Andre             Expires December 8, 2008               [Page 69]

Internet-Draft                   XMPP IM                       June 2008
   2.  "None + Pending Out" = contact and user are not subscribed to
       each other, and user has sent contact a subscription request but
       contact has not replied yet; this is reflected in the user's
       roster by subscription='none' and ask='subscribe'
   3.  "None + Pending In" = contact and user are not subscribed to each
       other, and contact has sent user a subscription request but user
       has not replied yet (note: contact's server SHOULD NOT push or
       deliver roster items in this state, but instead SHOULD wait until
       user has approved subscription request from contact); this is
       reflected in the user's roster by subscription='none'
   4.  "None + Pending Out+In" = contact and user are not subscribed to
       each other, contact has sent user a subscription request but user
       has not replied yet, and user has sent contact a subscription
       request but contact has not replied yet; this is reflected in the
       user's roster by subscription='none' and ask='subscribe'
   5.  "To" = user is subscribed to contact (one-way); this is reflected
       in the user's roster by subscription='to'
   6.  "To + Pending In" = user is subscribed to contact, and contact
       has sent user a subscription request but user has not replied
       yet; this is reflected in the user's roster by subscription='to'
   7.  "From" = contact is subscribed to user (one-way); this is
       reflected in the user's roster by subscription='from'
   8.  "From + Pending Out" = contact is subscribed to user, and user
       has sent contact a subscription request but contact has not
       replied yet; this is reflected in the user's roster by
       subscription='from' and ask='subscribe'
   9.  "Both" = user and contact are subscribed to each other (two-way);
       this is reflected in the user's roster by subscription='both'

A.2.  Server Processing of Outbound Presence Subscription Stanzas

   Outbound presence subscription stanzas enable the user to manage his
   or her subscription to the contact's presence (via the "subscribe"
   and "unsubscribe" types), and to manage the contact's access to the
   user's presence (via the "subscribed" and "unsubscribed" types).

   The following rules apply to outbound routing of the stanza as well
   as changes to the user's roster.

   Note: The rules for server processing of outbound presence
   subscription stanzas are described from the perspective of the user,
   not the contact.



Saint-Andre             Expires January 13, 2009               [Page 77]

Internet-Draft                   XMPP IM                       July 2008


   Note: In the following tables, "S.N." stand stands for SHOULD NOT.







Saint-Andre             Expires December 8, 2008               [Page 70]

Internet-Draft                   XMPP IM                       June 2008

A.2.1.  Subscribe

   Table 1: Processing of outbound "subscribe" stanzas

   +-----------------------------------------------------------------+
   |  EXISTING STATE          |  ROUTE?  |  NEW STATE                |
   +-----------------------------------------------------------------+
   |  "None"                  |  MUST    |  "None + Pending Out" [1]     |
   |  "None + Pending Out"    |  MUST    |  no state change          |
   |  "None + Pending In"     |  MUST    |  "None + Pending Out+In"  |
   |  "None + Pending Out+In" |  MUST    |  no state change          |
   |  "To"                    |  MUST    |  no state change          |
   |  "To + Pending In"       |  MUST    |  no state change          |
   |  "From"                  |  MUST    |  "From + Pending Out" [1]     |
   |  "From + Pending Out"    |  MUST    |  no state change          |
   |  "Both"                  |  MUST    |  no state change          |
   +-----------------------------------------------------------------+

   [1]

   Note: A state change to "pending out" includes setting the 'ask' flag
   to a value of "subscribe" in the user's roster.

A.2.2.  Unsubscribe

   Table 2: Processing of outbound "unsubscribe" stanzas

   +-----------------------------------------------------------------+
   |  EXISTING STATE          |  ROUTE?  |  NEW STATE                |
   +-----------------------------------------------------------------+
   |  "None"                  |  MUST    |  no state change          |
   |  "None + Pending Out"    |  MUST    |  "None"                   |
   |  "None + Pending In"     |  MUST    |  no state change          |
   |  "None + Pending Out+In" |  MUST    |  "None + Pending In"      |
   |  "To"                    |  MUST    |  "None"                   |
   |  "To + Pending In"       |  MUST    |  "Pending In"             |
   |  "From"                  |  MUST    |  no state change          |
   |  "From + Pending Out"    |  MUST    |  "From"                   |
   |  "Both"                  |  MUST    |  "From"                   |
   +-----------------------------------------------------------------+











Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 71] 78]

Internet-Draft                   XMPP IM                       June                       July 2008


A.2.3.  Subscribed

   Table 3: Processing of outbound "subscribed" stanzas

   +-----------------------------------------------------------------+
   |  EXISTING STATE          |  ROUTE?  |  NEW STATE                |
   +-----------------------------------------------------------------+
   |  "None"                  |  S.N.    |  no state change [1]      |
   |  "None + Pending Out"    |  S.N.    |  no state change          |
   |  "None + Pending In"     |  MUST    |  "From"                   |
   |  "None + Pending Out+In" |  MUST    |  "From + Pending Out"     |
   |  "To"                    |  S.N.    |  no state change          |
   |  "To + Pending In"       |  MUST    |  "Both"                   |
   |  "From"                  |  S.N.    |  no state change          |
   |  "From + Pending Out"    |  S.N.    |  no state change          |
   |  "Both"                  |  S.N.    |  no state change          |
   +-----------------------------------------------------------------+

   [1] A server MAY note the fact that the user wishes to allow the
   contact to be subscribed to the user's presence and automatically
   approve any subscription request received from the contact; if it
   does so, upon the receiving presence stanza of type "subscribed" from
   the user's client it MUST add a roster item for the contact to the
   user's roster and set the 'ask' flag to a value of "subscribed".
   However, the user's server still SHOULD NOT route the presence stanza
   of type "subscribed" to the contact.  This optional functionality
   applies only if the contact is not already in the user's roster or if
   the contact is in the user's roster with a state of "None" (not
   including a state of "None + Pending Out").

A.2.4.  Unsubscribed

   Table 4: Processing of outbound "unsubscribed" stanzas

   +-----------------------------------------------------------------+
   |  EXISTING STATE          |  ROUTE?  |  NEW STATE                |
   +-----------------------------------------------------------------+
   |  "None"                  |  S.N.    |  no state change          |
   |  "None + Pending Out"    |  S.N.    |  no state change          |
   |  "None + Pending In"     |  MUST    |  "None"                   |
   |  "None + Pending Out+In" |  MUST    |  "None + Pending Out"     |
   |  "To"                    |  S.N.    |  no state change          |
   |  "To + Pending In"       |  MUST    |  "To"                     |
   |  "From"                  |  MUST    |  "None"                   |
   |  "From + Pending Out"    |  MUST    |  "None + Pending Out"     |
   |  "Both"                  |  MUST    |  "To"                     |
   +-----------------------------------------------------------------+




Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 72] 79]

Internet-Draft                   XMPP IM                       June                       July 2008


A.3.  Server Processing of Inbound Presence Subscription Stanzas

   Inbound presence subscription stanzas request a subscription-related
   action from the user (via the "subscribe" type), inform the user of
   subscription-related actions taken by the contact (via the
   "unsubscribe" type), or enable the user to manage the contact's
   access to the user's presence information (via the "subscribed" and
   "unsubscribed" types).

   The following rules apply to delivery of the inbound stanza as well
   as changes to the user's roster.

   Note: The rules for server processing of inbound presence
   subscription stanzas are described from the perspective of the user,
   not the contact.

   Note: In the following tables, "S.N." stand for SHOULD NOT.

A.3.1.  Subscribe

   Table 5: Processing of inbound "subscribe" stanzas

   +------------------------------------------------------------------+
   |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
   +------------------------------------------------------------------+
   |  "None"                  |  MUST [1]  |  "None + Pending In"     |
   |  "None + Pending Out"    |  MUST      |  "None + Pending Out+In" |
   |  "None + Pending In"     |  S.N.      |  no state change         |
   |  "None + Pending Out+In" |  S.N.      |  no state change         |
   |  "To"                    |  MUST      |  "To + Pending In"       |
   |  "To + Pending In"       |  S.N.      |  no state change         |
   |  "From"                  |  S.N. [2]  |  no state change         |
   |  "From + Pending Out"    |  S.N. [2]  |  no state change         |
   |  "Both"                  |  S.N. [2]  |  no state change         |
   +------------------------------------------------------------------+

   [1] If the user previously sent presence of type "subscribed" as
   described under Appendix A.2.3, then the server MAY auto-reply with
   "subscribed" and change the state to "From" rather than "None +
   Pending In".

   [2] Server SHOULD auto-reply with "subscribed".

A.3.2.  Unsubscribe

   When the user's server receives a presence stanza of type
   "unsubscribe" for the user from the contact, if the stanza results in
   a subscription state change from the user's perspective then the



Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 73] 80]

Internet-Draft                   XMPP IM                       June                       July 2008


   user's server MUST change the state and SHOULD auto-reply by sending
   a presence stanza of type "unsubscribed" to the contact on behalf of
   the user.  Otherwise the user's server MUST NOT change the state and
   SHOULD NOT deliver the stanza.  These rules are summarized in the
   following table.

   Table 6: Processing of inbound "unsubscribe" stanzas

   +------------------------------------------------------------------+
   |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
   +------------------------------------------------------------------+
   |  "None"                  |  S.N.      |  no state change         |
   |  "None + Pending Out"    |  S.N.      |  no state change         |
   |  "None + Pending In"     |  S.N. [1]  |  "None"                  |
   |  "None + Pending Out+In" |  S.N. [1]  |  "None + Pending Out"    |
   |  "To"                    |  S.N.      |  no state change         |
   |  "To + Pending In"       |  S.N. [1]  |  "To"                    |
   |  "From"                  |  S.N. [1]  |  "None"                  |
   |  "From + Pending Out"    |  S.N. [1]  |  "None + Pending Out     |
   |  "Both"                  |  S.N. [1]  |  "To"                    |
   +------------------------------------------------------------------+

   [1] Server SHOULD auto-reply with "unsubscribed".

A.3.3.  Subscribed

   When the user's server receives a presence stanza of type
   "subscribed" for the user from the contact, if there is no pending
   outbound request for access to the contact's presence information,
   then it MUST NOT change the subscription state and SHOULD NOT deliver
   the stanza to the user.  If there is a pending outbound request for
   access to the contact's presence information and the inbound presence
   stanza of type "subscribed" results in a subscription state change,
   then the user's server MUST change the subscription state but SHOULD
   NOT deliver the stanza to the user.  If the user already has access
   to the contact's presence information, the inbound presence stanza of
   type "subscribed" does not result in a subscription state change;
   therefore the user's server MUST NOT change the subscription state
   and SHOULD NOT deliver the stanza to the user.  These rules are
   summarized in the following table.











Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 74] 81]

Internet-Draft                   XMPP IM                       June                       July 2008


   Table 7: Processing of inbound "subscribed" stanzas

   +------------------------------------------------------------------+
   |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
   +------------------------------------------------------------------+
   |  "None"                  |  S.N.      |  no state change         |
   |  "None + Pending Out"    |  S.N.      |  "To"                    |
   |  "None + Pending In"     |  S.N.      |  no state change         |
   |  "None + Pending Out+In" |  S.N.      |  "To + Pending In"       |
   |  "To"                    |  S.N.      |  no state change         |
   |  "To + Pending In"       |  S.N.      |  no state change         |
   |  "From"                  |  S.N.      |  no state change         |
   |  "From + Pending Out"    |  S.N.      |  "Both"                  |
   |  "Both"                  |  S.N.      |  no state change         |
   +------------------------------------------------------------------+

A.3.4.  Unsubscribed

   When the user's server receives a presence stanza of type
   "unsubscribed" for the user from the contact, if there is a pending
   outbound request for access to the contact's presence information or
   if the user currently has access to the contact's presence
   information, then the user's server MUST change the subscription
   state but SHOULD NOT deliver the stanza to the user.  Otherwise, the
   user's server MUST NOT change the subscription state and SHOULD NOT
   deliver the stanza.  These rules are summarized in the following
   table.

   Table 8: Processing of inbound "unsubscribed" stanzas

   +------------------------------------------------------------------+
   |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
   +------------------------------------------------------------------+
   |  "None"                  |  S.N.      |  no state change         |
   |  "None + Pending Out"    |  S.N.      |  "None"                  |
   |  "None + Pending In"     |  S.N.      |  no state change         |
   |  "None + Pending Out+In" |  S.N.      |  "None + Pending In"     |
   |  "To"                    |  S.N.      |  "None"                  |
   |  "To + Pending In"       |  S.N.      |  "None + Pending In"     |
   |  "From"                  |  S.N.      |  no state change         |
   |  "From + Pending Out"    |  S.N.      |  "From"                  |
   |  "Both"                  |  S.N.      |  "From"                  |
   +------------------------------------------------------------------+








Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 75] 82]

Internet-Draft                   XMPP IM                       June                       July 2008


Appendix B.  Blocking Communication

   Sections 2.3.5 and 5.4.10 of [IMP-REQS] require that a compliant
   instant messaging and presence technology must enable a user to block
   communications from selected users.  A protocol  Protocols for doing so is are
   specified in [XEP-0016]. [XEP-0016] and [XEP-0191].


Appendix C.  vCards

   Sections 3.1.3 and 4.1.4 of [IMP-REQS] require that it be possible to
   retrieve out-of-band contact information for other users (e.g.,
   telephone number or email address).  An XML representation of the
   vCard specification defined in RFC 2426 [VCARD] is in common use
   within the Jabber community to provide such information but is out of
   scope for XMPP this specification (documentation of this protocol is
   contained in [XEP-0054]).


Appendix D.  XML Schemas

   Because validation of XML streams and stanzas is optional, the
   following XML schemas are provided for descriptive purposes only.
   These schemas are not normative.

   The following schemas formally define various XML namespaces used in
   the core XMPP protocols, in conformance with [XML-SCHEMA].  For
   schemas defining namespaces for XML streams and other core aspects of
   XMPP, refer to [XMPP-CORE].

D.1.  jabber:client

   <?xml version='1.0' encoding='UTF-8'?>

   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='jabber:client'
       xmlns='jabber:client'
       elementFormDefault='qualified'>

     <xs:import
         namespace='urn:ietf:params:xml:ns:xmpp-stanzas'/>

     <xs:element name='message'>
        <xs:complexType>
           <xs:sequence>
             <xs:choice minOccurs='0' maxOccurs='unbounded'>
               <xs:element ref='subject'/>



Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 76] 83]

Internet-Draft                   XMPP IM                       June                       July 2008


               <xs:element ref='body'/>
               <xs:element ref='thread'/>
             </xs:choice>
             <xs:any     namespace='##other'
                         minOccurs='0'
                         maxOccurs='unbounded'/>
             <xs:element ref='error'
                         minOccurs='0'/>
           </xs:sequence>
           <xs:attribute name='from'
                         type='xs:string'
                         use='optional'/>
           <xs:attribute name='id'
                         type='xs:NMTOKEN'
                         use='optional'/>
           <xs:attribute name='to'
                         type='xs:string'
                         use='optional'/>
           <xs:attribute name='type'
                         use='optional'
                         default='normal'>
             <xs:simpleType>
               <xs:restriction base='xs:NCName'>
                 <xs:enumeration value='chat'/>
                 <xs:enumeration value='error'/>
                 <xs:enumeration value='groupchat'/>
                 <xs:enumeration value='headline'/>
                 <xs:enumeration value='normal'/>
               </xs:restriction>
             </xs:simpleType>
           </xs:attribute>
           <xs:attribute ref='xml:lang' use='optional'/>
        </xs:complexType>
     </xs:element>

     <xs:element name='body'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='xs:string'>
             <xs:attribute ref='xml:lang' use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:element name='subject'>
       <xs:complexType>
         <xs:simpleContent>



Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 77] 84]

Internet-Draft                   XMPP IM                       June                       July 2008


           <xs:extension base='xs:string'>
             <xs:attribute ref='xml:lang' use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:element name='thread' type='xs:NMTOKEN'/> name='thread'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='xs:NMTOKEN'>
             <xs:attribute name='parent'
                           type='xs:NMTOKEN'
                           use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:element name='presence'>
       <xs:complexType>
         <xs:sequence>
           <xs:choice minOccurs='0' maxOccurs='unbounded'>
             <xs:element ref='show'/>
             <xs:element ref='status'/>
             <xs:element ref='priority'/>
           </xs:choice>
           <xs:any     namespace='##other'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
           <xs:element ref='error'
                       minOccurs='0'/>
         </xs:sequence>
         <xs:attribute name='from'
                       type='xs:string'
                       use='optional'/>
         <xs:attribute name='id'
                       type='xs:NMTOKEN'
                       use='optional'/>
         <xs:attribute name='to'
                       type='xs:string'
                       use='optional'/>
         <xs:attribute name='type' use='optional'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='error'/>
               <xs:enumeration value='probe'/>
               <xs:enumeration value='subscribe'/>



Saint-Andre             Expires January 13, 2009               [Page 85]

Internet-Draft                   XMPP IM                       July 2008


               <xs:enumeration value='subscribed'/>
               <xs:enumeration value='unavailable'/>
               <xs:enumeration value='unsubscribe'/>
               <xs:enumeration value='unsubscribed'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>



Saint-Andre             Expires December 8, 2008               [Page 78]

Internet-Draft                   XMPP IM                       June 2008

     <xs:element name='show'>
       <xs:simpleType>
         <xs:restriction base='xs:NCName'>
           <xs:enumeration value='away'/>
           <xs:enumeration value='chat'/>
           <xs:enumeration value='dnd'/>
           <xs:enumeration value='xa'/>
         </xs:restriction>
       </xs:simpleType>
     </xs:element>

     <xs:element name='status'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='string1024'>
             <xs:attribute ref='xml:lang' use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:simpleType name='string1024'>
       <xs:restriction base='xs:string'>
         <xs:minLength value='1'/>
         <xs:maxLength value='1024'/>
       </xs:restriction>
     </xs:simpleType>

     <xs:element name='priority' type='xs:byte'/>

     <xs:element name='iq'>
       <xs:complexType>
         <xs:sequence>
           <xs:any     namespace='##other'
                       minOccurs='0'/>
           <xs:element ref='error'
                       minOccurs='0'/>



Saint-Andre             Expires January 13, 2009               [Page 86]

Internet-Draft                   XMPP IM                       July 2008


         </xs:sequence>
         <xs:attribute name='from'
                       type='xs:string'
                       use='optional'/>
         <xs:attribute name='id'
                       type='xs:NMTOKEN'
                       use='required'/>
         <xs:attribute name='to'
                       type='xs:string'
                       use='optional'/>
         <xs:attribute name='type' use='required'>



Saint-Andre             Expires December 8, 2008               [Page 79]

Internet-Draft                   XMPP IM                       June 2008
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='error'/>
               <xs:enumeration value='get'/>
               <xs:enumeration value='result'/>
               <xs:enumeration value='set'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='error'>
       <xs:complexType>
         <xs:sequence xmlns:err='urn:ietf:params:xml:ns:xmpp-stanzas'>
           <xs:group ref='err:stanzaErrorGroup'/>
           <xs:element ref='err:text'
                       minOccurs='0'/>
         </xs:sequence>
         <xs:attribute name='type' use='required'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='auth'/>
               <xs:enumeration value='cancel'/>
               <xs:enumeration value='continue'/>
               <xs:enumeration value='modify'/>
               <xs:enumeration value='wait'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
       </xs:complexType>
     </xs:element>

   </xs:schema>

D.2.  jabber:server



Saint-Andre             Expires January 13, 2009               [Page 87]

Internet-Draft                   XMPP IM                       July 2008


   <?xml version='1.0' encoding='UTF-8'?>

   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='jabber:server'
       xmlns='jabber:server'
       elementFormDefault='qualified'>

     <xs:import
         namespace='urn:ietf:params:xml:ns:xmpp-stanzas'/>



Saint-Andre             Expires December 8, 2008               [Page 80]

Internet-Draft                   XMPP IM                       June 2008

     <xs:element name='message'>
        <xs:complexType>
           <xs:sequence>
             <xs:choice minOccurs='0' maxOccurs='unbounded'>
               <xs:element ref='subject'/>
               <xs:element ref='body'/>
               <xs:element ref='thread'/>
             </xs:choice>
             <xs:any namespace='##other'
                     minOccurs='0'
                     maxOccurs='unbounded'/>
             <xs:element ref='error'
                         minOccurs='0'/>
           </xs:sequence>
           <xs:attribute name='from'
                         type='xs:string'
                         use='required'/>
           <xs:attribute name='id'
                         type='xs:NMTOKEN'
                         use='optional'/>
           <xs:attribute name='to'
                         type='xs:string'
                         use='required'/>
           <xs:attribute name='type'
                         use='optional'
                         default='normal'>
             <xs:simpleType>
               <xs:restriction base='xs:NCName'>
                 <xs:enumeration value='chat'/>
                 <xs:enumeration value='error'/>
                 <xs:enumeration value='groupchat'/>
                 <xs:enumeration value='headline'/>
                 <xs:enumeration value='normal'/>
               </xs:restriction>
             </xs:simpleType>
           </xs:attribute>
           <xs:attribute ref='xml:lang' use='optional'/>



Saint-Andre             Expires January 13, 2009               [Page 88]

Internet-Draft                   XMPP IM                       July 2008


        </xs:complexType>
     </xs:element>

     <xs:element name='body'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='xs:string'>
             <xs:attribute ref='xml:lang' use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>



Saint-Andre             Expires December 8, 2008               [Page 81]

Internet-Draft                   XMPP IM                       June 2008
     </xs:element>

     <xs:element name='subject'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='xs:string'>
             <xs:attribute ref='xml:lang' use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:element name='thread' type='xs:NMTOKEN'/> name='thread'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='xs:NMTOKEN'>
             <xs:attribute name='parent'
                           type='xs:NMTOKEN'
                           use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:element name='subject'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='xs:NMTOKEN'>
             <xs:attribute name='parent'
                           type='xs:NMTOKEN'
                           use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:element name='presence'>



Saint-Andre             Expires January 13, 2009               [Page 89]

Internet-Draft                   XMPP IM                       July 2008


       <xs:complexType>
         <xs:sequence>
           <xs:choice minOccurs='0' maxOccurs='unbounded'>
             <xs:element ref='show'/>
             <xs:element ref='status'/>
             <xs:element ref='priority'/>
           </xs:choice>
           <xs:any     namespace='##other'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
           <xs:element ref='error'
                       minOccurs='0'/>
         </xs:sequence>
         <xs:attribute name='from'
                       type='xs:string'
                       use='required'/>
         <xs:attribute name='id'
                       type='xs:NMTOKEN'
                       use='optional'/>
         <xs:attribute name='to'
                       type='xs:string'
                       use='required'/>



Saint-Andre             Expires December 8, 2008               [Page 82]

Internet-Draft                   XMPP IM                       June 2008
         <xs:attribute name='type' use='optional'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='error'/>
               <xs:enumeration value='probe'/>
               <xs:enumeration value='subscribe'/>
               <xs:enumeration value='subscribed'/>
               <xs:enumeration value='unavailable'/>
               <xs:enumeration value='unsubscribe'/>
               <xs:enumeration value='unsubscribed'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='show'>
       <xs:simpleType>
         <xs:restriction base='xs:NCName'>
           <xs:enumeration value='away'/>
           <xs:enumeration value='chat'/>
           <xs:enumeration value='dnd'/>
           <xs:enumeration value='xa'/>
         </xs:restriction>
       </xs:simpleType>



Saint-Andre             Expires January 13, 2009               [Page 90]

Internet-Draft                   XMPP IM                       July 2008


     </xs:element>

     <xs:element name='status'>
       <xs:complexType>
         <xs:simpleContent>
           <xs:extension base='string1024'>
             <xs:attribute ref='xml:lang' use='optional'/>
           </xs:extension>
         </xs:simpleContent>
       </xs:complexType>
     </xs:element>

     <xs:simpleType name='string1024'>
       <xs:restriction base='xs:string'>
         <xs:minLength value='1'/>
         <xs:maxLength value='1024'/>
       </xs:restriction>
     </xs:simpleType>

     <xs:element name='priority' type='xs:byte'/>

     <xs:element name='iq'>



Saint-Andre             Expires December 8, 2008               [Page 83]

Internet-Draft                   XMPP IM                       June 2008
       <xs:complexType>
         <xs:sequence>
           <xs:any namespace='##other'
                   minOccurs='0'/>
           <xs:element ref='error'
                       minOccurs='0'/>
         </xs:sequence>
         <xs:attribute name='from'
                       type='xs:string'
                       use='required'/>
         <xs:attribute name='id'
                       type='xs:NMTOKEN'
                       use='required'/>
         <xs:attribute name='to'
                       type='xs:string'
                       use='required'/>
         <xs:attribute name='type' use='required'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='error'/>
               <xs:enumeration value='get'/>
               <xs:enumeration value='result'/>
               <xs:enumeration value='set'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>



Saint-Andre             Expires January 13, 2009               [Page 91]

Internet-Draft                   XMPP IM                       July 2008


         <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='error'>
       <xs:complexType>
         <xs:sequence xmlns:err='urn:ietf:params:xml:ns:xmpp-stanzas'>
           <xs:group ref='err:stanzaErrorGroup'/>
           <xs:element ref='err:text'
                       minOccurs='0'/>
         </xs:sequence>
         <xs:attribute name='type' use='required'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='auth'/>
               <xs:enumeration value='cancel'/>
               <xs:enumeration value='continue'/>
               <xs:enumeration value='modify'/>
               <xs:enumeration value='wait'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>



Saint-Andre             Expires December 8, 2008               [Page 84]

Internet-Draft                   XMPP IM                       June 2008
       </xs:complexType>
     </xs:element>

   </xs:schema>

D.3.  jabber:iq:roster

   <?xml version='1.0' encoding='UTF-8'?>

   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='jabber:iq:roster'
       xmlns='jabber:iq:roster'
       elementFormDefault='qualified'>

     <xs:element name='query'>
       <xs:complexType>
         <xs:sequence>
           <xs:element ref='item'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
         </xs:sequence>
       </xs:complexType>
     </xs:element>

     <xs:element name='item'>



Saint-Andre             Expires January 13, 2009               [Page 92]

Internet-Draft                   XMPP IM                       July 2008


       <xs:complexType>
         <xs:sequence>
           <xs:element ref='group'
                       minOccurs='0'
                       maxOccurs='unbounded'/>
         </xs:sequence>
         <xs:attribute name='ask' use='optional'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='subscribe'/>
               <xs:enumeration value='subscribed'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute name='jid' type='xs:string' use='required'/>
         <xs:attribute name='name' type='xs:string' use='optional'/>
         <xs:attribute name='subscription' use='optional'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='both'/>
               <xs:enumeration value='from'/>
               <xs:enumeration value='none'/>



Saint-Andre             Expires December 8, 2008               [Page 85]

Internet-Draft                   XMPP IM                       June 2008
               <xs:enumeration value='remove'/>
               <xs:enumeration value='to'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
       </xs:complexType>
     </xs:element>

     <xs:element name='group' type='xs:string'/>

   </xs:schema>


Appendix E.  Differences From RFC 3921

   Based on consensus derived from implementation and deployment
   experience as well as formal interoperability testing, the following
   substantive modifications were made from RFC 3921.

   o  The protocol for session establishment was determined to be
      unnecessary and therefore the content previously defined in
      Section 3 of RFC 3921 was removed.  However, for the sake of
      backward-compatibility server implementations are encouraged to
      advertise support for the feature, even though session
      establishment is a "no-op".
   o  The protocol for communications blocking specified in Section 10
      of RFC 3921 has been moved to [XEP-0016].




Saint-Andre             Expires January 13, 2009               [Page 93]

Internet-Draft                   XMPP IM                       July 2008


   o  In order to more seamlessly repair lack of synchronization in
      subscription states between rosters located at different servers,
      error handling related to presence probes and presence
      notifications was modified to return presence stanzas of type
      "unsubscribe" or "unsubscribed" rather than error stanzas.
   o  Added optional server support for pre-approved presence
      subscriptions via presence stanzas of type "subscribed" and the
      optional "subscribed" value for the 'ask' flag.
   o  Added optional 'parent' attribute to <thread/> element
   o  The protocol for communications blocking specified in Section 10
      of RFC 3921 has been moved to [XEP-0016].

   In addition, numerous changes of an editorial nature were made in
   order to more fully specify and clearly explain the protocols.


Appendix F.  Copying Conditions

   Regarding this entire document or any portion of it, the author makes
   no guarantees and is not responsible for any damage resulting from
   its use.  The author grants irrevocable permission to anyone to use,
   modify, and distribute it in any way that does not diminish the
   rights of anyone else to use, modify, and distribute it, provided
   that redistributed derivative works do not contain misleading author



Saint-Andre             Expires December 8, 2008               [Page 86]

Internet-Draft                   XMPP IM                       June 2008
   or version information.  Derivative works need not be licensed under
   similar terms.


Index

   A
      Available Resource  32

   B
      Broadcasted Presence  31  37

   C
      Chat Session  51  52
      Contact  20  24

   D
      Directed Presence  31  37

   I
      Initial Presence  31
      Interested Resource  11  37

   O
      Offline Message Storage  62  69

   P
      Presence  5  7



Saint-Andre             Expires January 13, 2009               [Page 94]

Internet-Draft                   XMPP IM                       July 2008


      Presence Broadcast  37
      Presence Probe  33  39
      Presence Session  31  37
      Presence Subscription  20  24

   R
      Roster  5  7
      Roster Get  8  11
      Roster Push  9  12
      Roster Result  10  13
      Roster Set  9  11

   S
      Subscription Request  21  25

   U
      Unavailable Presence  37







Saint-Andre             Expires December 8, 2008               [Page 87]

Internet-Draft                   XMPP IM                       June 2008  43


Author's Address

   Peter Saint-Andre (editor)
   XMPP Standards Foundation

   Email: stpeter@jabber.org
   URI:   https://stpeter.im/

























Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 88] 95]

Internet-Draft                   XMPP IM                       June                       July 2008


Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights 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; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.











Saint-Andre             Expires December 8, 2008 January 13, 2009               [Page 89] 96]

----