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Versions: (draft-miller-xmpp-im) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 RFC 3921

Network Working Group                                     P. Saint-Andre
Internet-Draft                                                 J. Miller
Expires: October 20, 2003                     Jabber Software Foundation
                                                          April 21, 2003


                         XMPP Instant Messaging
                         draft-ietf-xmpp-im-09

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at http://
   www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on October 20, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document describes the specific extensions to and applications
   of the Extensible Messaging and Presence Protocol (XMPP) that are
   required to create a basic instant messaging and presence
   application, such as the servers and clients that comprise the Jabber
   network.









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Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  4
   1.1   Overview . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   1.2   Requirements . . . . . . . . . . . . . . . . . . . . . . . .  4
   1.3   Terminology  . . . . . . . . . . . . . . . . . . . . . . . .  5
   1.4   Discussion Venue . . . . . . . . . . . . . . . . . . . . . .  5
   1.5   Intellectual Property Notice . . . . . . . . . . . . . . . .  5
   2.    Establishing a Session . . . . . . . . . . . . . . . . . . .  6
   3.    Exchanging Messages  . . . . . . . . . . . . . . . . . . . .  8
   3.1   Specifying an Intended Recipient . . . . . . . . . . . . . .  8
   3.2   Specifying a Message Type  . . . . . . . . . . . . . . . . .  8
   3.3   Specifying a Message Subject . . . . . . . . . . . . . . . .  9
   3.4   Specifying a Conversation Thread . . . . . . . . . . . . . .  9
   3.5   Specifying a Message Body  . . . . . . . . . . . . . . . . . 10
   3.6   Specifying Additional Information  . . . . . . . . . . . . . 10
   3.7   Message-Related Errors . . . . . . . . . . . . . . . . . . . 11
   4.    Exchanging Presence Information  . . . . . . . . . . . . . . 12
   4.1   Client and Server Responsibilities . . . . . . . . . . . . . 12
   4.2   Sending Initial Presence . . . . . . . . . . . . . . . . . . 13
   4.3   Specifying Availability Status . . . . . . . . . . . . . . . 13
   4.4   Specifying Detailed Status Information . . . . . . . . . . . 13
   4.5   Probing for Presence . . . . . . . . . . . . . . . . . . . . 14
   4.6   Sending Final Presence . . . . . . . . . . . . . . . . . . . 14
   4.7   Determining When a Contact Went Offline  . . . . . . . . . . 14
   5.    Managing Subscriptions . . . . . . . . . . . . . . . . . . . 16
   5.1   Requesting a Subscription  . . . . . . . . . . . . . . . . . 16
   5.2   Handling a Subscription Request  . . . . . . . . . . . . . . 16
   5.3   Cancelling a Subscription from Another Entity  . . . . . . . 17
   5.4   Unsubscribing from Another Entity's Presence . . . . . . . . 17
   6.    Managing One's Roster  . . . . . . . . . . . . . . . . . . . 18
   6.1   Retrieving One's Roster on Login . . . . . . . . . . . . . . 18
   6.2   Adding a Roster Item . . . . . . . . . . . . . . . . . . . . 19
   6.3   Deleting a Roster Item . . . . . . . . . . . . . . . . . . . 21
   7.    Integration of Roster Items and Presence Subscriptions . . . 22
   7.1   Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 22
   7.2   User Subscribes to Contact . . . . . . . . . . . . . . . . . 22
   7.2.1 Alternate Flow . . . . . . . . . . . . . . . . . . . . . . . 25
   7.3   Creating a Mutual Subscription . . . . . . . . . . . . . . . 26
   7.3.1 Alternate Flow . . . . . . . . . . . . . . . . . . . . . . . 28
   7.4   Unsubscribing  . . . . . . . . . . . . . . . . . . . . . . . 29
   7.4.1 Case #1: Subscription Type 'to'  . . . . . . . . . . . . . . 29
   7.4.2 Case #2: Subscription Type 'both'  . . . . . . . . . . . . . 31
   7.5   Cancelling a Subscription  . . . . . . . . . . . . . . . . . 33
   7.5.1 Case #1: Subscription Type 'from'  . . . . . . . . . . . . . 33
   7.5.2 Case #2: Subscription Type 'both'  . . . . . . . . . . . . . 34
   7.6   Removing a Roster Item and Cancelling All Subscriptions  . . 36
   8.    Blocking Communication . . . . . . . . . . . . . . . . . . . 37



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   8.1   Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
   8.2   Business Rules . . . . . . . . . . . . . . . . . . . . . . . 39
   8.3   Retrieving One's Privacy Lists . . . . . . . . . . . . . . . 40
   8.4   Managing Active Lists  . . . . . . . . . . . . . . . . . . . 43
   8.5   Managing the Default List  . . . . . . . . . . . . . . . . . 45
   8.6   Editing a Privacy List . . . . . . . . . . . . . . . . . . . 46
   8.7   Removing a Privacy List  . . . . . . . . . . . . . . . . . . 47
   8.8   Blocking Messages  . . . . . . . . . . . . . . . . . . . . . 47
   8.9   Blocking Inbound Presence Notifications  . . . . . . . . . . 49
   8.10  Blocking Outbound Presence Notifications . . . . . . . . . . 51
   8.11  Blocking IQs . . . . . . . . . . . . . . . . . . . . . . . . 52
   8.12  Blocking All Communication . . . . . . . . . . . . . . . . . 54
   8.13  Blocked Entity Attempts to Communicate with User . . . . . . 55
   8.14  Higher-Level Heuristics  . . . . . . . . . . . . . . . . . . 56
   9.    Routing and Delivery Rules . . . . . . . . . . . . . . . . . 58
   9.1   Client Generation of To Addresses  . . . . . . . . . . . . . 58
   9.2   Server Handling of XML Stanzas . . . . . . . . . . . . . . . 58
   10.   IANA Considerations  . . . . . . . . . . . . . . . . . . . . 60
   10.1  XML Namespace Name for Session Data  . . . . . . . . . . . . 60
   11.   Security Considerations  . . . . . . . . . . . . . . . . . . 61
         Normative References . . . . . . . . . . . . . . . . . . . . 62
         Informative References . . . . . . . . . . . . . . . . . . . 63
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 63
   A.    vCards . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
   B.    XML Schemas  . . . . . . . . . . . . . . . . . . . . . . . . 65
   B.1   session  . . . . . . . . . . . . . . . . . . . . . . . . . . 65
   B.2   jabber:iq:last . . . . . . . . . . . . . . . . . . . . . . . 65
   B.3   jabber:iq:privacy  . . . . . . . . . . . . . . . . . . . . . 65
   B.4   jabber:iq:privacy:error  . . . . . . . . . . . . . . . . . . 67
   B.5   jabber:iq:roster . . . . . . . . . . . . . . . . . . . . . . 67
   C.    Revision History . . . . . . . . . . . . . . . . . . . . . . 69
   C.1   Changes from draft-ietf-xmpp-im-08 . . . . . . . . . . . . . 69
   C.2   Changes from draft-ietf-xmpp-im-07 . . . . . . . . . . . . . 69
   C.3   Changes from draft-ietf-xmpp-im-06 . . . . . . . . . . . . . 69
   C.4   Changes from draft-ietf-xmpp-im-05 . . . . . . . . . . . . . 69
   C.5   Changes from draft-ietf-xmpp-im-04 . . . . . . . . . . . . . 70
   C.6   Changes from draft-ietf-xmpp-im-03 . . . . . . . . . . . . . 70
   C.7   Changes from draft-ietf-xmpp-im-02 . . . . . . . . . . . . . 70
   C.8   Changes from draft-ietf-xmpp-im-01 . . . . . . . . . . . . . 70
   C.9   Changes from draft-ietf-xmpp-im-00 . . . . . . . . . . . . . 70
   C.10  Changes from draft-miller-xmpp-im-02 . . . . . . . . . . . . 71
         Full Copyright Statement . . . . . . . . . . . . . . . . . . 72









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1. Introduction

1.1 Overview

   The core features of the Extensible Messaging and Presence Protocol
   are defined in XMPP Core [1].  These features -- specifically XML
   streams, stream authentication and encryption, and the <message/>,
   <presence/>, and <iq/> children of the stream root -- provide the
   building blocks for many types of near-real-time applications, which
   may be layered on top of the core by sending application-specific
   data scoped by particular XML namespaces.  This document describes
   the extensions to and applications of XMPP Core that are required to
   create the basic functionality expected of an instant messaging and
   presence application as defined in RFC 2779 [2].

1.2 Requirements

   For the purposes of this document, we stipulate that a basic instant
   messaging and presence application needs to enable a user to perform
   the following high-level use cases:

   o  Establish a session with a server

   o  Exchange messages with other users

   o  Exchange presence information with other users

   o  Manage subscriptions to and from other users

   o  Manage the items in the user's contact list (in XMPP this is
      called a "roster")

   o  Block communications to or from specific other users

   Detailed definitions of these functionality areas are contained in
   RFC 2779 [2], and the interested reader is directed to that document
   regarding the requirements addressed herein.

   Note: although XMPP IM meets the requirements of RFC 2779, it was not
   designed explicitly with RFC 2779 in mind, since the base protocol
   evolved through an open development process within the Jabber open-
   source community, mainly in 1999.  In addition, protocols addressing
   many other functionality areas have been defined and continue to be
   defined by the Jabber Software Foundation [5].  These include service
   discovery, multi-user chat, data gathering and forms submission,
   feature negotiation, message composing events, message expiration,
   delayed delivery, file transfer, XHTML message formatting, publish-
   subscribe, and transports for XML-RPC and SOAP.  However, such



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   protocols are not described herein because they are not required by
   RFC 2779 [2].

1.3 Terminology

   This document inherits the terminology defined in XMPP Core [1].

   The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
   "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [3].

1.4 Discussion Venue

   The authors welcome discussion and comments related to the topics
   presented in this document.  The preferred forum is the
   <xmppwg@jabber.org> mailing list, for which archives and subscription
   information are available at <http://www.jabber.org/cgi-bin/mailman/
   listinfo/xmppwg/>.

1.5 Intellectual Property Notice

   This document is in full compliance with all provisions of Section 10
   of RFC 2026.  Parts of this specification use the term "jabber" for
   identifying namespaces and other protocol syntax.  Jabber[tm] is a
   registered trademark of Jabber, Inc.  Jabber, Inc.  grants permission
   to the IETF for use of the Jabber trademark in association with this
   specification and its successors, if any.























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2. Establishing a Session

   Most instant messaging applications based on XMPP are implemented via
   a client-server architecture that requires a user to establish a
   session on the server in order to engage in standard instant
   messaging and presence activities.  However, there are several pre-
   conditions that must be met before a user may establish such a
   session.  These include:

   1.  Account Provisioning -- while this is outside the scope of XMPP,
       methods for doing so include account creation by a server
       administrator as well as in-band account registration using the
       'jabber:iq:register' namespace; the latter method is documented
       by the Jabber Software Foundation [5] at <http://www.jabber.org/
       protocol/>.

   2.  Authentication and Resource Authorization -- methods for
       completing these pre-conditions are documented in XMPP Core [1];
       note that client authentication with a server MUST include an
       authorization identity that specifies the full JID (user@domain/
       resource) associated with the connection for addressing purposes.

   Once a client has authenticated with a server and authorized a full
   JID (including resource), it SHOULD request that the server activate
   an IM session for the client.  This is accomplished by means of the
   'urn:ietf:params:xml:ns:xmpp-session' namespace:

   Step 1: Client requests session with server:

   <iq type='set' id='sess_1'>
     <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
   </iq>

   Step 2: Server informs client that session has been created:

   <iq type='result' id='sess_1'/>

   Several error conditions are possible.  For example, the server may
   encounter an internal condition that prevents it from creating the
   session, the username or authorization identity may lack permissions
   to create a session, or there may already be an active session
   associated with an authzid of the same name.

   If the server encounters an internal condition that prevents it from
   creating the session, it MUST return an error.






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   Step 2 (alt): Server responds with error (internal server error):

   <iq type='error' id='sess_1'>
     <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
     <error class='server'>
       <condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
         <internal-server-error/>
       </condition>
     </error>
   </iq>

   If the username or authorization identity is not allowed to create a
   session, the server MUST return an error.

   Step 2 (alt): Server responds with error (username or authzid not
   allowed to create session):

   <iq type='error' id='sess_1'>
     <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
     <error class='access'>
       <condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
         <not-allowed/>
       </condition>
     </error>
   </iq>

   If there is already an active session associated with an authzid of
   the same name, the server MUST either (1) terminate the active
   session and allow the newly-requested session, or (2) disallow the
   newly-requested session and maintain the existing session.  Which of
   these the server does is up to the implementation, although it is
   RECOMMENDED to implement (1).

   Step 2 (alt): Server informs client of resource conflict (the desired
   resource name is already in use by another active connection):

   <iq type='error' id='sess_1'>
     <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
     <error class='access'>
       <condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
         <conflict/>
       </condition>
     </error>
   </iq>







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3. Exchanging Messages

   Exchanging messages is a basic use of XMPP and is effected when a
   user sends a message stanza to another user (or, more generally,
   another entity).  As defined under Routing and Delivery Rules
   (Section 9), the sender's server is responsible for delivering the
   message to the intended recipient (if the recipient is on the same
   server) or for routing the message to the recipient's server (if the
   recipient is on a different server).

   Detailed information regarding the syntax of message stanzas and
   their defined attributes and child elements may be found in XMPP Core
   [1].

3.1 Specifying an Intended Recipient

   A client SHOULD specify an intended recipient for the message by
   providing an appropriate JID in the 'to' attribute of the <message/>
   element.  Normally, the value of the 'to' attribute specifies an
   entity other than the sending user (see Section 9 for exceptions).
   The intended recipient MAY be any valid JID (a user on the same
   server, a user on a different server, the server itself, another
   server, etc.).  If the JID is invalid or cannot be contacted, the
   entity discovering that fact (usually the sender's or recipient's
   server) MUST return an error to the sender.

3.2 Specifying a Message Type

   As mentioned in XMPP Core [1], there are several defined types of
   messages (specified by means of a 'type' attribute within the
   <message/> element).  In the context of an instant messaging
   application, a client MAY include a message type in order to capture
   the conversational context of the message, thus providing a hint
   regarding presentation (e.g., in a GUI).  If no 'type' attribute is
   provided, the message SHOULD be assumed to be a standalone message to
   which the recipient MAY reply if desired.  If the 'type' attribute is
   included, it SHOULD have one of the following values (any other value
   MAY be ignored):

   o  chat -- The message is sent in the context of a one-to-one chat
      conversation.  A compliant client SHOULD present an interface
      enabling one-to-one chat between the two parties, including an
      appropriate conversation history.

   o  groupchat -- The message is sent in the context of a multi-user
      chat environment.  A compliant client SHOULD present an interface
      enabling many-to-many chat between the parties, including a roster
      of parties in the chatroom and an appropriate conversation



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      history.

   o  headline -- The message is probably generated by an automated
      service that delivers or broadcasts content (news, sports, market
      information, RSS feeds, etc.).  No reply to the message is
      expected, and a compliant client SHOULD present an interface that
      appropriately differentiates the message from standalone messages,
      chat sessions, or groupchat sessions (e.g., by not providing the
      recipient with the ability to reply).

   o  error -- An error has occurred related to a previous message sent
      by the sender (for details regarding stanza error syntax, see XMPP
      Core [1]).  A compliant client SHOULD present an appropriate
      interface informing the sender of the nature of the error.

   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').

3.3 Specifying a Message Subject

   A message stanza MAY contain a child <subject/> element specifying
   the subject of the message.  The subject MUST NOT contain mixed
   content.  Multiple <subject/> elements MAY be included, as long as
   each contains an 'xml:lang' attribute with a distinct value.

   A message with a subject:

   <message to='romeo@montague.net' from="juliet@capulet.com/balcony'>
     <subject>Imploring</subject>
     <body>Wherefore art thou, Romeo?</body>
   </message>


3.4 Specifying a Conversation Thread

   A message stanza MAY contain a child <thread/> element specifying the
   conversation thread in which the message is situated, for the purpose
   of tracking the conversation.  The content of the <thread/> element
   is a random string that is generated by the sender in accordance with
   the algorithm specified in XMPP Core [1]; this string SHOULD be
   copied back to the sender in subsequent replies.







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   A threaded conversation:

   <message
       to='romeo@montague.net/orchard'
       from='juliet@capulet.com/balcony'
       type='chat'>
     <body>Art thou not Romeo, and a Montague?</body>
     <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
   </message>

   <message
       to='juliet@capulet.com/balcony'
       from='romeo@montague.net/orchard'
       type='chat'>
     <body>Neither, fair saint, if either thee dislike.</body>
     <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
   </message>

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


3.5 Specifying a Message Body

   A message stanza MAY (and often will) contain a child <body/> element
   specifying the main content of the message as CDATA.  The body MUST
   NOT contain mixed content.  If it is necessary to provide the main
   message content in an alternate form (e.g., encrypted using the
   public key infrastructure or formatted using XHTML), the alternate
   form MUST be contained in an appropriately-namespaced child of the
   message stanza, as defined for any such extended namespace.  Multiple
   <body/> elements MAY be included, as long as each contains an
   'xml:lang' attribute with a distinct value.

3.6 Specifying Additional Information

   A message stanza MAY house an element containing content that extends
   the meaning of the message (e.g., an encrypted form of the message
   body).  In common usage this child element is often the <x/> element
   but MAY be any element, as long as the 'xmlns' namespace declaration
   is something other than the streams namespace or the default
   namespace; this extended namespace defines all elements contained
   within the child element.



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3.7 Message-Related Errors

   If a message sent by a sender cannot be delivered, the entity
   discovering that fact (usually either the sender's or recipient's
   server) MUST return that message to the sender in a message stanza of
   type "error" along with an appropriate error message (for details
   regarding stanza error syntax, see XMPP Core [1])

   A message-related error:

   <message
       to='romeo@montague.net'
       from='juliet@capulet.com'
       type='error'>
     <body>Sleep dwell upon thine eyes.</body>
     <error class='address'>
       <condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
         <jid-not-found/>
       </condition>
     </error>
   </message>






























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4. Exchanging Presence Information

   Exchanging presence information is made relatively straightforward
   within XMPP by using presence stanzas.  However, we see here a
   contrast to the handling of messages: although a client MAY send
   directed presence information to another entity, in general presence
   information is sent from a client to a server (with no 'to' address)
   and then broadcasted by the server to any entities that are
   subscribed to the presence of the sending entity.  (Note: in the
   terminology of RFC 2778 [4], the only watchers in XMPP are
   subscribers.)

   Detailed information regarding the syntax of presence stanzas and
   their defined attributes and child elements may be found in XMPP Core
   [1].

4.1 Client and Server Responsibilities

   When a client connects to a server, it SHOULD send an initial
   presence stanza to the server to express default availability.  This
   presence stanza MUST possess no 'to' address (signalling that it is
   meant to be handled by the server on behalf of the user) and SHOULD
   have no type.

   Upon receiving initial presence from a client, the server MUST send
   presence probes from the full JID (user@domain/resource) of the user
   to any remote entities that are subscribed to the user's presence (as
   represented in the user's roster) in order to determine if they are
   available.  (The remote server is responsible for responding to the
   presence probe only when (1) the probing entity has been allowed to
   access the probed entity's presence, e.g., by server rules or user
   subscriptions, and (2) the probed entity is available.  The probing
   entity's server then informs the probing entity of the probed
   entity's last known available presence, for all of the probed
   entity's resources if applicable.)

   Throughout the active session of a connected resource, the server is
   responsible for broadcasting any changes in the availability status
   of the connected resource to the subscribed entities that are
   available, so that such entities are kept apprised of availability
   changes.

   Finally, when a connected resource becomes unavailable, the server
   MUST notify all of the subscribed entities that are available, as
   well as any entities to which the user sent directed presence during
   the active session for that connected resource.





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4.2 Sending Initial Presence

   Upon authenticating, a client SHOULD send initial presence to its
   server indicating that the connected resource is available for
   communications.  This presence stanza MUST have no 'to' address and
   SHOULD have no type.

   Initial presence sent from client to server:

   <presence/>


4.3 Specifying Availability Status

   A client MAY provide further information about its availability
   status by using the <show/> element.  As mentioned in XMPP Core [1],
   the recognized values for the show element are:

   o  away -- The entity or resource is temporarily away.

   o  chat -- The entity or resource is actively interested in chatting.

   o  xa -- The entity or resource is away for an extended period (xa =
      "eXtended Away").

   o  dnd -- The entity or resource is busy (dnd = "Do Not Disturb").

   Availability status:

   <presence>
     <show>away</show>
   </presence>

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

4.4 Specifying Detailed Status Information

   In conjunction with the  <show/> element, a client MAY provide
   detailed status information by using the <status/> element.  The
   content of this element is a natural-language description of the
   client's current availability status.









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   Detailed status information:

   <presence>
     <show>dnd</show>
     <status>Busy fighting the Romans</status>
   </presence>


4.5 Probing for Presence

   A server MAY probe for the current presence of another entity.  A
   user or client SHOULD NOT send presence stanzas of type 'probe'.

4.6 Sending Final Presence

   Upon ending its session with a server, a client SHOULD gracefully
   become unavailable by sending a final presence stanza that is
   explicitly of type unavailable.

   Sending final presence to express unavailable state:

   <presence type='unavailable'/>

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

   The server MUST NOT depend on receiving final presence from a
   connected resource, since the resource may become unavailable
   unexpectedly.  If a server detects that a resource has become
   unavailable for any reason (either gracefully or ungracefully), it
   MUST send <presence type="unavailable"/> to all online entities that
   are subscribed to the associated user's presence, as well as to any
   entities to which the user sent directed presence during the active
   session for that connected resource.

4.7 Determining When a Contact Went Offline

   The server MUST maintain a record of the time at which a user became
   unavailable (whether gracefully or ungracefully).  An authorized
   subscriber to that user's presence MAY determine the time of last
   activity by sending an IQ stanza to the user's bare JID (user@domain)
   containing an empty <query/> element scoped by the 'jabber:iq:last'
   namespace:








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   Requesting the last active time of a user:

   <iq type='get' to='user@domain'>
     <query xmlns='jabber:iq:last'/>
   </iq>

   If the entity requesting the time of last activity is an authorized
   subscriber to the user's presence, the server SHOULD return an IQ
   stanza of type 'result' with the number of seconds since the user was
   last active (subject to service provisioning and privacy
   configuration at a particular deployment):

   Returning the last active time of a user:

   <iq from='user@domain' type='result' to='subscriber@domain/resource'>
     <query seconds='76490' xmlns='jabber:iq:last'/>
   </iq>

   If the entity requesting the time of last activity is not an
   authorized subscriber to the user's presence, the server MUST return
   an IQ stanza of type 'error' with an error condition of forbidden:

   Requester is forbidden to view the last active time of a user:

   <iq from='user@domain' type='result' to='subscriber@domain/resource'>
     <query xmlns='jabber:iq:last'/>
     <error class='access'>
       <condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
         <forbidden/>
       </condition>
     </error>
   </iq>



















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5. Managing Subscriptions

   In order to protect the privacy of instant messaging users and any
   other entities, presence and availability information is made
   available only to other entities that the user has approved.  When a
   user has agreed that another entity may view its presence, the entity
   is said to have a subscription to the user's presence information.  A
   subscription lasts across sessions; indeed, it lasts until the
   subscriber unsubscribes or the subscribee cancels the previously-
   granted subscription.  Subscriptions are managed within XMPP by
   sending presence stanzas containing specially-defined attributes.

   Note: there are important interactions between subscriptions and
   rosters; these are defined under Integration of Roster Items and
   Presence Subscriptions (Section 7), and the reader must refer to that
   section for a complete understanding of presence subscriptions.

5.1 Requesting a Subscription

   A request to subscribe to another entity's presence is made by
   sending a presence stanza of type "subscribe".

   Sending a subscription request:

   <presence to='juliet@capulet.com' type='subscribe'/>


5.2 Handling a Subscription Request

   When a client receives a subscription request from another entity, it
   MAY accept the request by sending a presence stanza of type
   "subscribed" or decline the request by sending a presence stanza of
   type "unsubscribed".

   Accepting a subscription request:

   <presence to='romeo@montague.net' type='subscribed'/>

   Denying a presence subscription request:

   <presence to='romeo@montague.net' type='unsubscribed'/>

   A user's server MUST NOT automatically accept subscription requests
   on the user's behalf.  All subscription requests MUST be directed to
   the user's client.  If there is no connected resource associated with
   the user when the subscription request is received, the user's server
   MUST store the subscription request offline for delivery when the
   user next becomes available.



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5.3 Cancelling a Subscription from Another Entity

   If a user would like to cancel a previously-granted subscription
   request, it sends a presence stanza of type "unsubscribed".

   Cancelling a previously granted subscription request:

   <presence to='romeo@montague.net' type='unsubscribed'/>


5.4 Unsubscribing from Another Entity's Presence

   If a user would like to unsubscribe from the presence of another
   entity, it sends a presence stanza of type "unsubscribe".

   Unsubscribing from an entity's presence:

   <presence to='juliet@capulet.com' type='unsubscribe'/>

































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6. Managing One's Roster

   In XMPP, one's contact list is called a roster.  A roster is stored
   by the server on the user's behalf so that the user may access roster
   information from any connected resource.

   Note: there are important interactions between rosters and
   subscriptions; these are defined under Integration of Roster Items
   and Presence Subscriptions (Section 7), and the reader must refer to
   that section for a complete understanding of roster management.

6.1 Retrieving One's Roster on Login

   Upon connecting to the server, a client MAY request the roster
   (however, because receiving the roster may not be desirable for all
   resources, e.g., a connection with limited bandwidth, the client's
   request for the roster is OPTIONAL).  If a connected resource does
   not request the roster during a session, it SHOULD never receive
   presence subscriptions and associated roster pushes.

   Client requests current roster from server:

   <iq type='get' id='roster_1'>
     <query xmlns='jabber:iq:roster'/>
   </iq>


























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   Client receives roster from the server:

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


6.2 Adding a Roster Item

   At any time, a user MAY add an item to his or her roster.

   Client adds a new item:

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

   The server is responsible for updating the roster information in
   persistent storage, and also for pushing that change out to all
   connected resources associated with the user using an IQ stanza of
   type "set" (this is referred to as a "roster push").  This "roster



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   push" enables all connected resources to remain in sync with the
   server-based roster information.

   Server replies with an IQ result to the sending resource and pushes
   the updated roster information to all connected resources:

   <iq
       from='capulet.com'
       to='juliet@capulet.com/balcony'
       type='result'
       id='roster_2'/>
   <iq
       from='capulet.com'
       to='juliet@capulet.com/balcony'
       type='set'/>
     <query xmlns='jabber:iq:roster'>
       <item
           name='Nurse'
           jid='nurse@capulet.com'
           subscription='none'>
         <group>Servants</group>
       </item>
     </query>
   </iq>
   <iq
       from='capulet.com'
       to='juliet@capulet.com/chamber'
       type='set'/>
     <query xmlns='jabber:iq:roster'>
       <item
           name='Nurse'
           jid='nurse@capulet.com'
           subscription='none'>
         <group>Servants</group>
       </item>
     </query>
   </iq>














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   Connected resources reply with an IQ result to the server:

   <iq
       from='juliet@capulet.com/balcony'
       to='capulet.com'
       type='result'/>
   <iq
       from='juliet@capulet.com/chamber'
       to='capulet.com'
       type='result'/>

   Updating an existing roster item (e.g., changing the group) is done
   in the same way as adding a new roster item, i.e., by sending the
   roster item in an IQ set to the server.

6.3 Deleting a Roster Item

   At any time, a user MAY delete an item from its roster by doing an IQ
   set and making sure that the value of the 'subscription' attribute is
   "remove" (a compliant server MUST ignore any other values of the
   'subscription' attribute when received from a client).

   Client removes an item:

   <iq type='set' id='roster_2'>
     <query xmlns='jabber:iq:roster'>
       <item
           name='Nurse'
           jid='nurse@capulet.com'
           subscription='remove'>
         <group>Servants</group>
       </item>
     </query>
   </iq>

   As with adding a roster item, when deleting a roster item the server
   is responsible for updating the roster information in persistent
   storage, and also for initiating a "roster push" to all connected
   resources associated with the user.

   For further information about the implications of this command, see
   Section 7.6.









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7. Integration of Roster Items and Presence Subscriptions

7.1 Overview

   Some level of integration between roster items and presence
   subscriptions is normally expected by instant messaging users.  This
   section describes the level of integration that must be supported
   within XMPP IM.

   There are four primary subscription states:

   o  None -- Neither the user nor the contact is subscribed to the
      other's presence

   o  To -- The user is subscribed to the contact's presence but there
      is no subscription from the contact to the user

   o  From -- There is a subscription from the contact to the user, but
      the user has not subscribed to the contact's presence

   o  Both -- Both the user and the contact are subscribed to each
      other's presence (i.e., the union of 'from' and 'to')

   Each of these states is reflected in the roster of both the user and
   the contact, thus resulting in durable subscription states.  The
   details regarding how these subscription states interact with roster
   items is explained in the following sub-sections.

   As noted above, if a connected resource does not request the roster
   during a session, it SHOULD never receive presence subscriptions and
   the associated roster pushes.  In addition, a client MUST acknowledge
   each roster push with an IQ stanza of type "result" (these stanzas
   are not shown in the following examples but are required by XMPP Core
   [1]).

7.2 User Subscribes to Contact

   The process by which a user subscribes to a contact, including the
   interaction between roster items and subscription states, is defined
   below.

   1.  In preparation for being able to render the contact in the user's
       client interface and for the server to keep track of the
       subscription, the user's client SHOULD send an IQ stanza of
       type='set' in the 'jabber:iq:roster' namespace for the new roster
       item; the <item/> element MUST possess a 'jid' attribute, MAY
       possess a 'name' attribute, may contain one or more <group/>
       child, and MUST NOT posses a 'subscription' attribute:



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   <iq type='set' id='int1'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@domain'
           name='MyContact'/>
     </query>
   </iq>

   2.  The server then MUST (1) reply with an IQ stanza of type='result'
       and (2) initiate a "roster push" for the new roster item to all
       connected resources associated with this user, setting the
       subscription state set to 'none':

   <iq
       type='result'
       to='user@domain/resource'
       id='int1'/>

   <iq type='set' to='user@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@domain'
           name='MyContact'
           subscription='none'/>
     </query>
   </iq>

   3.  In order to initiate the subscription, the user's client MUST
       then send a presence stanza of type='subscribe' to the contact
       (the user's client must also acknowledge the roster push):

   <presence to='contact@domain' type='subscribe'/>

   4.  The server MUST then initiate a second "roster push" to all
       connected resources associated with the user, setting the contact
       to the pending sub-state of the 'none' subscription state; this
       pending sub-state is denoted by the inclusion of the
       ask='subscribe' attribute in the roster item:













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   <iq type='set' to='user@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@domain'
           name='MyContact'
           subscription='none'
           ask='subscribe'/>
     </query>
   </iq>

       Note: if the user did not create a roster item before sending the
       subscription request, the server MUST create one and send the
       above roster push to all of the user's connected resources.

   5.  The server MUST also deliver the presence stanza to the contact
       or route it to the contact's server for delivery to the contact,
       first stamping the stanza with the user's bare JID as the 'from'
       address:

   <presence
       to='contact@domain'
       from='user@domain'
       type='subscribe'/>

   6.  If the contact is online (i.e., there is a connected resource
       associated with the contact's account), the contact must now
       decide whether or not to accept the subscription request.  (If
       the contact is offline, the contact's server MUST store the
       subscription request offline for delivery when the contact next
       becomes available.) Here we will assume the "happy path" that the
       contact accepts the subscription, in which case the contact's
       client MAY send a roster set to the server specifying the desired
       nickname and group for the user, and MUST send a presence stanza
       of type='subscribed' to the user.

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@domain'
           name='SomeUser'/>
     </query>
   </iq>

   <presence to='user@domain' type='subscribed'/>

   7.  The contact's server MUST now initiate a "roster push" to all
       connected resources associated with the contact, containing a
       roster item for the user with the subscription state set to



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       'from':

   <iq type='set' to='contact@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@domain'
           name='SomeUser'
           subscription='from'/>
     </query>
   </iq>

   8.  As a result of the fact that the contact has accepted the
       subscription request, the user's server MUST (1) deliver the
       presence stanza of type='subscribed' from the contact to the
       user, and (2) initiate a "roster push" to all connected resources
       associated with the user, containing an updated roster item for
       the contact with the subscription type set to a value of "to":

   <presence
       to='user@domain'
       type='subscribed'
       from='contact@domain'/>

   <iq type='set' to='user@domain/resource'>
     <query xmlns='jabber:iq:roster'>
     <item
         jid='contact@domain'
         name='MyContact'
         subscription='to'/>
     </query>
   </iq>

   From the perspective of the user, there is now a subscription to the
   contact; from the perspective of the contact, there is now a
   subscription from the user.  The contact's server MUST now send the
   contact's current presence information to the user.  (Note: If at
   this point the user sends another subscription request to the
   contact, the user's server MUST "swallow" that request and not send
   it on the contact.)

7.2.1 Alternate Flow

   The above activity flow represents the "happy path" related to the
   user's subscription request to the contact.  The main alternate flow
   occurs if the contact denies the user's subscription request; in
   order to deny the request, the contact's client MUST send a presence
   stanza of type "unsubscribed" to the user:




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   <presence to='user@domain' type='unsubscribed'/>

   The user's server MUST then (1) deliver that presence stanza to the
   user and (2) initiate a "roster push" to all connected resources
   associated with the user, with the subscription attribute set to a
   value of "none":

   <presence
       to='user@domain'
       type='unsubscribed'
       from='contact@domain'/>

   <iq type='set' to='user@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@domain'
           name='MyContact'
           subscription='none'/>
     </query>
   </iq>

   As a result of this activity, the contact is now in the user's roster
   with a subscription state of "none", whereas the user is not in the
   contact's roster at all.

7.3 Creating a Mutual Subscription

   The user and contaact can build on the foregoing to create a mutual
   subscription (i.e., a subscription of type "both").  The process is
   defined below.

   1.  If the contact desires a mutual subscription, the contact MUST
       send a subscription request to the user (subject to user
       preferences, the contact's client MAY send this automatically):

   <presence to='user@domain' type='subscribe'/>

   2.  The contact's server MUST then initiate a "roster push" to all
       connected resources associated with the contact, with the user
       still in the 'from' subscription state but with a pending 'to'
       subscription denoted by the inclusion of the ask='subscribe'
       attribute in the roster item:









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   <iq type='set' to='contact@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@domain'
           name='SomeUser'
           subscription='from'
           ask='subscribe'/>
     </query>
   </iq>

   3.  If the user is online (i.e., there is a connected resource
       associated with the user's account), the user must now decide
       whether or not to accept the subscription request.  (If the user
       is offline, the user's server MUST store the subscription request
       offline for delivery when the user next becomes available.) Here
       we will assume the "happy path" that the user accepts the
       subscription, in which case the user's client MUST send a
       presence stanza of type='subscribed' to the contact.

   <presence to='contact@domain' type='subscribed'/>

   4.  The user's server MUST then initiate a "roster push" to all
       connected resources associated with the user, containing a roster
       item for the contact with the subscription attribute set to a
       value of "both":

   <iq type='set' to='user@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@domain'
           name='MyContact'
           subscription='both'/>
     </query>
   </iq>

   5.  As a result of the fact that the user has accepted the
       subscription request, the contact's server MUST (1) deliver the
       presence stanza of type='subscribed' from the user to the
       contact, and (2) initiate a "roster push" to all connected
       resources associated with the contact, containing an updated
       roster item for the user with the subscription type set to a
       value of "both":









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   <presence
       to='contact@domain'
       from='user@domain'
       type='subscribed'/>

   <iq type='set' to='contact@domain/resource'>
     <query xmlns='jabber:iq:roster'>
     <item
         jid='user@domain'
         name='SomeUser'
         subscription='both'/>
     </query>
   </iq>

   The user and the contact now have a mutual subscription to each
   other's presence -- i.e., the subscription is of type 'both'.  The
   user's server MUST now send the user's current presence information
   to the contact.  (Note: If at this point the user sends a
   subscription request to the contact or the contact sends a
   subscription request to the user, the sending user's server will
   "swallow" that request and not send it on the intended recipient.)

7.3.1 Alternate Flow

   The above activity flow represents the "happy path" related to the
   contact's subscription request to the user.  The main alternate flow
   occurs if the user denies the contact's subscription request; in
   order to deny the request, the user's client MUST send a presence
   stanza of type "unsubscribed" to the contact:

   <presence to='contact@domain' type='unsubscribed'/>

   The contact's server MUST then (1) deliver that presence stanza to
   the contact and (2) initiate a "roster push" to all connected
   resources associated with the contact, with the subscription
   attribute set to a value of "from" and with no 'ask' attribute:















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   <presence
       to='contact@domain'
       from='user@domain'
       type='unsubscribed'/>

   <iq type='set' to='contact@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@domain'
           name='SomeUser'
           subscription='from'/>
     </query>
   </iq>

   As a result of this activity, there has been no change in the
   subscription state; i.e., the contact is in the user's roster with a
   subscription state of "to" and the user is in the contact's roster
   with a subscription state of "from".

7.4 Unsubscribing

   At any time after subscribing to a contact's presence, a user MAY
   unsubscribe.  While the XML that the user sends to make this happen
   is the same in all instances, the subsequent subscription state is
   different depending on the subscription state obtaining when the
   unsubscribe command is sent.  Both possible scenarios are defined
   below.

7.4.1 Case #1: Subscription Type 'to'

   In the first case, the user has a subscription to the contact but the
   contact does not have a subscription to the user (i.e., the
   subscription is not yet mutual).

   1.  In order to unsubscribe from the contact's presence, the user
       MUST send a presence stanza of type "unsubscribe" to the contact:

   <presence to='contact@domain' type='unsubscribe'/>

   2.  As a result, the user's server MUST send a "roster push" to each
       connected resource associated with the user, containing a roster
       item for the contact with the 'subscription' attribute set to a
       value of "from":








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   <iq type='set' to='user@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@domain'
           name='MyContact'
           subscription='from'/>
     </query>
   </iq>

   3.  The user's server MUST also route the unsubscribe "command" to
       the contact's server:

   <presence
       to='contact@domain'
       from='user@domain'
       type='unsubscribe'/>

   4.  The contact's server MUST initiate a "roster push" to all
       connected resources associated with the contact, containing a
       roster item for the user with the 'subscription' attribute set to
       a value of "to" (if the contact is offline, the contact's server
       MUST modify the roster item and send that modified item the next
       time the contact requests the roster); the contact's server
       SHOULD also deliver the unsubscribe command to the contact:

   <iq type='set' to='contact@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@domain'
           name='SomeUser'
           subscription='to'/>
     </query>
   </iq>

   <presence
       to='contact@domain'
       from='user@domain'
       type='unsubscribe'/>

   5.  The contact's server then MUST send unavailable presence from the
       contact to the user and MAY send a presence stanza of type
       "unsubscribed" to the user:









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   <presence
       to='user@domain'
       from='contact@domain'
       type='unavailable'/>

   <presence
       to='user@domain'
       from='contact@domain'
       type='unsubscribed'/>

   6.  As a result, the user's server MUST deliver the unavailable
       presence from the user to the contact and (if received) the
       presence stanza of type "unsubscribed" from the contact to the
       user,

   <presence
       to='user@domain'
       from='contact@domain'
       type='unavailable'/>

   <presence
       to='user@domain'
       from='contact@domain'
       type='unsubscribed'/>


7.4.2 Case #2: Subscription Type 'both'

   In the second case, the user has a subscription to the contact and
   the contact also has a subscription to the user.

   1.  In order to unsubscribe from the contact's presence, the user
       MUST send a presence stanza of type "unsubscribe" to the contact:

   <presence to='contact@domain' type='unsubscribe'/>

   2.  As a result, the user's server MUST send a "roster push" to each
       connected resource associated with the user, containing a roster
       item for the contact with the 'ask' attribute set to unsubscribe
       to indicate that the unsubscribe is pending:











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   <iq type='set' to='user@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@domain'
           name='MyContact'
           subscription='both'
           ask='unsubscribe'/>
     </query>
   </iq>

   3.  Since the unsubscribe command does not normally need to be
       approved by the contact, the contact's server then SHOULD auto-
       reply on behalf of the contact by sending a presence stanza of
       type "unsubscribed" to the user; additionally, it MUST send
       unavailable presence from the contact to the user:

   <presence
       to='user@domain'
       from='contact@domain'
       type='unsubscribed'/>

   <presence
       to='user@domain'
       from='contact@domain'
       type='unavailable'/>

   4.  The contact's server also MUST initiate a "roster push" to all
       connected resources associated with the contact, containing a
       roster item for the user with the 'subscription' attribute set to
       a value of "to" (if the contact is offline, the contact's server
       MUST modify the roster item and send that modified item the next
       time the contact requests the roster):

   <iq type='set' to='contact@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@domain'
           name='SomeUser'
           subscription='to'/>
     </query>
   </iq>

   5.  As a result, the user's server MUST (1) deliver the presence
       stanza of type='unsubscribed' from the contact to the user, (2)
       initiate a "roster push" to all connected resources associated
       with the user, containing an updated roster item for the contact
       with the subscription type set to a value of "from" and with no
       'ask' attribute, and (3) deliver the unavailable presence from



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       the user to the contact:

   <presence
       to='user@domain'
       from='contact@domain'
       type='unsubscribed'/>

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@domain'
           subscription='none'
           name='MyContact'/>
     </query>
   </iq>

   <presence
       to='user@domain'
       from='contact@domain'
       type='unavailable'/>

   Note: Obviously this does not result in removal of the roster item
   from the user's roster, and the contact still has a subscription to
   the user's presence.  In order to more completely cancel a mutual
   subscription and fully remove the roster item from the user's roster,
   the user should update the roster item with subscription='remove' as
   defined in Section 7.6.

7.5 Cancelling a Subscription

   At any time after approving a subscription request from a user, a
   contact MAY cancel that subscription.  While the XML that the contact
   sends to make this happen is the same in all instances, the
   subsequent subscription state is different depending on the
   subscription state obtaining when the cancellation is sent.  Both
   possible scenarios are defined below.

7.5.1 Case #1: Subscription Type 'from'

   In the first case, the user has a subscription to the contact but the
   contact does not have a subscription to the user (i.e., the
   subscription is not yet mutual).

   1.  In order to cancel the user's subscription, the contact MUST send
       a presence stanza of type "unsubscribed" to the user:

   <presence to='user@domain' type='unsubscribed'/>




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   2.  As a result, the contact's server MUST (1) send a "roster push"
       to each connected resource associated with the contact,
       containing a roster item for the user with the 'subscription'
       attribute set to a value of "none", and (2) send unavailable
       presence from the contact to the user:

   <iq type='set' to='contact@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@domain'
           name='SomeUser'
           subscription='none'/>
     </query>
   </iq>

   <presence
       to='user@domain'
       from='contact@domain'
       type='unavailable'/>

   3.  The user's server MUST then initiate a "roster push" to all
       connected resources associated with the user, containing a roster
       item for the contact with the 'subscription' attribute set to a
       value of "none" (if the user is offline, the user's server MUST
       modify the roster item and send that modified item the next time
       the user requests the roster); additionally, it MUST also deliver
       the unavailable presence from the contact to the user:

   <iq type='set' to='user@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@domain'
           name='MyContact'
           subscription='none'/>
     </query>
   </iq>

   <presence
       to='user@domain'
       from='contact@domain'
       type='unavailable'/>


7.5.2 Case #2: Subscription Type 'both'

   In the second case, the user has a subscription to the contact and
   the contact also has a subscription to the user.




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   1.  In order to cancel the user's subscription, the user MUST send a
       presence stanza of type "unsubscribed" to the user:

   <presence to='user@domain' type='unsubscribed'/>

   2.  As a result, the contact's server MUST (1) send a "roster push"
       to each connected resource associated with the contact,
       containing a roster item for the user with the 'subscription'
       attribute set to a value of "to", and (2) send unavailable
       presence from the contact to the user:

   <iq type='set' to='contact@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='user@domain'
           name='SomeUser'
           subscription='to'/>
     </query>
   </iq>

   <presence
       to='user@domain'
       from='contact@domain'
       type='unavailable'/>

   3.  The user's server MUST then initiate a "roster push" to all
       connected resources associated with the user, containing a roster
       item for the contact with the 'subscription' attribute set to a
       value of "from" (if the user is offline, the user's server MUST
       modify the roster item and send that modified item the next time
       the user requests the roster); additionally, it MUST also deliver
       the unavailable presence from the contact to the user:

   <iq type='set' to='user@domain/resource'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@domain'
           name='MyContact'
           subscription='from'/>
     </query>
   </iq>

   <presence
       to='user@domain'
       from='contact@domain'
       type='unavailable'/>

   Note: Obviously this does not result in removal of the roster item



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   from the contact's roster, and the contact still has a subscription
   to the user's presence.  In order to more completely cancel a mutual
   subscription and fully remove the roster item from the contact's
   roster, the contact should update the roster item with
   subscription='remove' as defined in Section 7.6.

7.6 Removing a Roster Item and Cancelling All Subscriptions

   Because there may be many steps involved in completely removing a
   roster item and reverting the subscription state to "none", XMPP IM
   includes a "shortcut" method for doing so.  The process may be
   initiated by either a contact or a user no matter what the current
   subscription state is, by means of sending a roster set with the
   subscription attribute set to a value of "remove".

   For example, a user may send the following XML:

   <iq type='set'>
     <query xmlns='jabber:iq:roster'>
       <item
           jid='contact@domain'
           name='MyContact'
           subscription='remove'/>
     </query>
   </iq>

   When the user removes a contact from his or her roster by setting the
   'subscription' attribute to a value of "remove", the user's server
   MUST automatically cancel any existing presence subscription between
   the user and the contact by sending presence stanzas of type
   "unsubscribe" and "unsubscribed" from the user to the contact.

   A contact may also send such a command, resulting in the same type of
   system behavior.

















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8. Blocking Communication

   Most instant messaging systems have found it necessary to implement
   some method for users to block communications from particular other
   users (this is also required by sections 5.1.5, 5.1.15, 5.3.2, and
   5.4.10 of RFC 2779 [2]).  In XMPP this is done using the
   'jabber:iq:privacy' namespace by managing one's privacy lists.

   Server-side privacy lists enable successful completion of the
   following use cases:

   o  Retrieving one's privacy lists.

   o  Adding, removing, and editing one's privacy lists.

   o  Setting, changing, or declining active lists.

   o  Setting, changing, or declining the default list (i.e., the list
      that is active by default).

   o  Allowing or denying messages based on JID, group, or subscription
      type (or globally).

   o  Allowing or denying inbound presence notifications based on JID,
      group, or subscription type (or globally).

   o  Allowing or denying outbound presence notifications based on JID,
      group, or subscription type (or globally).

   o  Allowing or denying IQs based on JID, group, or subscription type
      (or globally).

   o  Allowing or denying all communications based on JID, group, or
      subscription type (or globally).

   Note: presence notifications do not include presence subscriptions,
   only presence information that is broadcasted to entities that are
   subscribed to a user's presence information.  Thus this includes
   presence stanzas with no 'type' attribute or of type='unavailable'
   only.

8.1 Syntax

   A user may define one or more privacy lists, which are stored by the
   user's server.  Each <list/> element contains one or more rules in
   the form of <item/> elements, and each <item/> element uses
   attributes to define a privacy rule type, a specific value within the
   type, the relevant action, and the place of the item in the



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   processing order.

   The syntax is as follows:

   <iq>
     <query xmlns='jabber:iq:privacy'>
       <list name='foo'>
         <item
             type='[jid|group|subscription]'
             value='bar'
             action='[accept|deny]'
             order='nonNegativeInteger'/>
       </list>
     </query>
   </iq>

   If the type is "jid", then the 'value' attribute MUST contain a valid
   Jabber ID.  JIDs are matched in the following order: "user@domain/
   resource", then "user@domain", then "domain/resource", then "domain".
   If the value is "user@domain", then any connected resource for that
   user@domain matches.  If the value is "domain", then any user@domain
   matches.  If the value is "domain/resource", then only that resource
   matches.

   If the type is "group", then the 'value' attribute MUST contain the
   name of a group in the user's roster.

   If the type is "subscription", then the 'value' attribute MUST be one
   of "both", "to", "from", or "none" as defined in XMPP Core [1].

   If no 'type' attribute is included, the rule provides the "fall-
   through" case.

   The 'action' attribute MUST be included and its value MUST be either
   "accept" or "deny".

   The 'order' attribute MUST be included and its value MUST be a non-
   negative integer that is unique among all items in the list.  (If a
   client attempts to create or update a list with non-unique order
   values, the server MUST return to the client a <bad-request/> error
   of class "format" in the 'urn:ietf:params:xml:ns:xmpp-stanzas'
   namespace.)

   Within the 'jabber:iq:privacy' namespace, the <query/> child of a
   client-generated IQ stanza of type "set" MUST NOT include more than
   one child element (i.e., the stanza must contain only one <active/>
   element, one <default/> element, or one <list/> element); if a client
   violates this rule, the server MUST return to the client a <bad-



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   request/> error of class "format" in the
   'urn:ietf:params:xml:ns:xmpp-stanzas' namespace.)

   When a client adds or updates a privacy list, the <list/> element
   MUST contain at least one <item/> child element.

   When a client updates a privacy list, it must include all of the
   desired items (i.e., not a "delta").

8.2 Business Rules

   The active list affects only the session/resource for which it is
   activated, and only for the duration of the session.  If a stanza is
   addressed to a specific resource, only the active list for that
   session is processed (i.e., the default list is ignored).

   The default list applies to the user as a whole, and is processed if
   there is no active list set for the target session/resource to which
   a stanza is addressed, or if there are no current sessions for the
   user.

   If there is no active list set for a session (or there are no current
   sessions for the user), and there is no default list, then all
   stanzas SHOULD BE accepted or appropriately processed by the server
   on behalf of the user.

   Privacy lists SHOULD be the first routing and delivery rule applied
   by a server, trumping the other rules specified in Section 9.

   The order in which privacy list items are processed by the server is
   important.  List items MUST be processed in ascending order
   determined by the values of the 'order' attribute for each <item/>.

   As soon as a stanza is matched against a privacy list, the server
   SHOULD appropriately handle the stanza and cease processing.

   If no fall-through item is provided in a list, the fall-through
   action is assumed to be "accept".

   When a user updates the definition for a list or adds a new list
   (whether or not it is active), the server SHOULD NOT "push" that
   information out to all connected resources associated with the user's
   account, as is done for rosters.  If a client or user wants to
   retrieve the current privacy list information, it SHOULD request the
   relevant list.






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8.3 Retrieving One's Privacy Lists

   Client requests names of privacy lists from server:

   <iq type='get' id='getlist1'>
     <query xmlns='jabber:iq:privacy'/>
   </iq>

   Server sends names of privacy lists to client, including default list
   and active list:

   <iq type='result' id='getlist1' to='romeo@montague.net/orchard'>
     <query xmlns='jabber:iq:privacy'>
       <active name='private'/>
       <default name='public'/>
       <list name='public'/>
       <list name='private'/>
       <list name='special'/>
     </query>
   </iq>

   Client requests a privacy list from server:

   <iq type='get' id='getlist2'>
     <query xmlns='jabber:iq:privacy'>
       <list name='public'/>
     </query>
   </iq>

   Server sends a privacy list to client:

   <iq type='result' id='getlist2' to='romeo@montague.net/orchard'>
     <query xmlns='jabber:iq:privacy'>
       <list name='public'>
         <item jid='tybalt@capulet.com' action='deny' order='1'/>
         <item action='allow' order='2'/>
       </list>
     </query>
   </iq>












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   Client requests another privacy list from server:

   <iq type='get' id='getlist3'>
     <query xmlns='jabber:iq:privacy'>
       <list name='private'/>
     </query>
   </iq>

   Server sends another privacy list to client:

   <iq type='result' id='getlist3' to='romeo@montague.net/orchard'>
     <query xmlns='jabber:iq:privacy'>
       <list name='private'>
         <item type='subscription' value='both'
               action='allow' order='10'/>
         <item action='deny' order='15'/>
       </list>
     </query>
   </iq>

   Client requests yet another privacy list from server:

   <iq type='get' id='getlist4'>
     <query xmlns='jabber:iq:privacy'>
       <list name='special'/>
     </query>
   </iq>
























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   Server sends yet another privacy list to client:

   <iq type='result' id='getlist4' to='romeo@montague.net/orchard'>
     <query xmlns='jabber:iq:privacy'>
       <list name='special'>
         <item
             type='jid'
             value='juliet@capulet.com'
             action='allow'
             order='6'/>
         <item
             type='jid'
             value='benvolio@shakespeare.lit'
             action='allow'
             order='7'/>
         <item
             type='jid'
             value='mercutio@shakespeare.lit'
             action='allow'
             order='42'/>
         <item action='deny'/>
       </list>
     </query>
   </iq>

   In this example, the user has three lists: (1) 'public', which allows
   communications from everyone except one specific entity; (2)
   'private', which allows communications only from contacts who have a
   bi-directional subscription with the user; and (3) 'special', which
   allows communications only from three specific entities.  The active
   list currently being applied by the server is the 'private' list.

   If the user attempts to retrieve a list but a list by that name does
   not exist, the server MUST return an application-specific "list not
   found" error to the user:
















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   Client attempts to retrieve non-existent list:

   <iq type='result' id='getlist5'>
     <query xmlns='jabber:iq:privacy'>
       <list name='The Empty Set'/>
     </query>
     <error class='app'>
       <condition xmlns='jabber:iq:privacy:error'>
         <list-not-found/>
       </condition>
     </error>
   </iq>

   The user may retrieve only one list at a time.  If the user attempts
   to retrieve more than one list in the same request, the server MUST
   return an application-specific <too-many-lists/> error to the user.

   Client attempts to retrieve more than one list:

   <iq type='result' id='getlist6'>
     <query xmlns='jabber:iq:privacy'>
       <list name='public'/>
       <list name='private'/>
       <list name='special'/>
     </query>
     <error class='app'>
       <condition xmlns='jabber:iq:privacy:error'>
         <too-many-lists/>
       </condition>
     </error>
   </iq>


8.4 Managing Active Lists

   In order to set or change the active list currently being applied by
   the server, the user MUST send an IQ stanza of type 'set' with a
   <query/> element scoped by the 'jabber:iq:privacy' namespace that
   contains an empty <active/> child element possessing a 'name'
   attribute whose value is set to the desired list name.











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   Client requests change of active list:

   <iq type='set' id='active1'>
     <query xmlns='jabber:iq:privacy'>
       <active name='special'/>
     </query>
   </iq>

   The server MUST activate and apply the requested list before sending
   the result back to the client.

   Server acknowledges success of active list change:

   <iq type='result' id='active1' to='juliet@capulet.com/balcony'/>

   If the user attempts to set an active list but a list by that name
   does not exist, the server MUST return an application-specific "list
   not found" error to the user:

   Client attempts to set a non-existent list as active:

   <iq type='result' id='active2'>
     <query xmlns='jabber:iq:privacy'>
       <list name='The Empty Set'/>
     </query>
     <error class='app'>
       <condition xmlns='jabber:iq:privacy:error'>
         <list-not-found/>
       </condition>
     </error>
   </iq>

   In order to decline the use of any active list (i.e., to use the
   domain's stanza routing rules for the duration of the session), a
   user MUST send an empty <active/> element with no name.

   Client declines the use of active lists:

   <iq type='set' id='active2'>
     <query xmlns='jabber:iq:privacy'>
       <active/>
     </query>
   </iq>








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8.5 Managing the Default List

   In order to change the default list associated with an account, the
   user MUST send an IQ stanza of type 'set' with a <query/> element
   scoped by the 'jabber:iq:privacy' namespace that contains an empty
   <default/> child element possessing a 'name' attribute whose value is
   set to the desired list name.

   Client requests change of default list:

   <iq type='set' id='default1'>
     <query xmlns='jabber:iq:privacy'>
       <default name='special'/>
     </query>
   </iq>

   Server acknowledges success of default list change:

   <iq type='result' id='default1' to='juliet@capulet.com/balcony'/>

   If the user attempts to set a default list but a list by that name
   does not exist, the server MUST return an application-specific "list
   not found" error to the user:

   Client attempts to set a non-existent list as default:

   <iq type='result' id='default2'>
     <query xmlns='jabber:iq:privacy'>
       <list name='The Empty Set'/>
     </query>
     <error class='app'>
       <condition xmlns='jabber:iq:privacy:error'>
         <list-not-found/>
       </condition>
     </error>
   </iq>

   In order to decline the use of a default list (i.e., to use the
   domain's stanza routing rules at all times), a user MUST send an
   empty <default/> element with no name.











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   Client declines the use of the default list:

   <iq type='set' id='default2'>
     <query xmlns='jabber:iq:privacy'>
       <default/>
     </query>
   </iq>


8.6 Editing a Privacy List

   In order to edit a privacy list, the user MUST send an IQ stanza of
   type 'set' with a <query/> element scoped by the 'jabber:iq:privacy'
   namespace that contains one <list/> child element possessing a 'name'
   attribute whose value is set to the list name the user would like to
   edit.  The <list/> element MUST contain one or more <item/> elements,
   which specify the user's desired changes to the list by including all
   elements in the list (not the "delta"); the same protocol is used to
   create a new list.

   Client edits a privacy list:

   <iq type='set' id='edit1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='public'>
         <item type='jid' value='tybalt@capulet.com'
               action='deny' order='3'/>
         <item type='jid' value='paris@shakespeare.lit'
               action='deny' order='5'/>
         <item action='allow' order='68'/>
       </list>
     </query>
   </iq>

   Note: The value of the 'order' attribute for any given item is not
   fixed.  Thus in the foregoing example if the user would like to add 4
   items between the "tybalt@capulet.com" item and the
   "paris@shakespeare.lit" item, the user's client can simply renumber
   all the items before submitting the list to the server.

   Server acknowledges success of list edit:

   <iq type='result' id='edit1' to='juliet@capulet.com/balcony'/>

   In this example, the user has added one additional entity to the
   "blacklist" portion of this privacy list.





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8.7 Removing a Privacy List

   In order to remove a privacy list, the user MUST send an IQ stanza of
   type 'set' with a <query/> element scoped by the 'jabber:iq:privacy'
   namespace that contains one empty <list/> child elements possessing a
   'name' attribute whose value is set to the list name the user would
   like to remove.

   Client removes a privacy list:

   <iq type='set' id='remove1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='private'/>
     </query>
   </iq>

   Server acknowledges success of list removal:

   <iq type='result' id='remove1' to='juliet@capulet.com/balcony'/>

   If a user attempts to remove an active list or the default list, the
   server MUST return an application-specific <cannot-be-removed/> error
   to the user.

   If the user attempts to remove a list but a list by that name does
   not exist, the server MUST return an application-specific <list-not-
   found/> error to the user.

   If the user attempts to remove more than one list in the same
   request, the server MUST return an application-specific <too-many-
   lists/> error to the user.

8.8 Blocking Messages

   Server-side privacy lists enable a user to block incoming messages
   from other users based on the other user's JID, roster group, or
   subscription status, or globally.  The following examples illustrate
   the required protocol.













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   User blocks based on JID:

   <iq type='set' id='msg1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='message-jid-example'>
         <item type='jid' value='tybalt@capulet.com'
               action='deny' order='3'>
           <message/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive messages from the user with the specified JID.

   User blocks based on roster group:

   <iq type='set' id='msg2'>
     <query xmlns='jabber:iq:privacy'>
       <list name='message-group-example'>
         <item type='group' value='Enemies' action='deny' order='4'>
           <message/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive messages from any users in the specified roster
   group.

   User blocks based on subscription type:

   <iq type='set' id='msg3'>
     <query xmlns='jabber:iq:privacy'>
       <list name='message-sub-example'>
         <item type='subscription' value='none' action='deny' order='5'>
           <message/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive messages from any users with the specified
   subscription type.




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   User blocks globally:

   <iq type='set' id='msg4'>
     <query xmlns='jabber:iq:privacy'>
       <list name='message-global-example'>
         <item action='deny' order='6'>
           <message/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive messages from any other users.

8.9 Blocking Inbound Presence Notifications

   Server-side privacy lists enable a user to block incoming presence
   notifications from other users based on the other user's JID, roster
   group, or subscription status, or globally.  The following examples
   illustrate the required protocol.

   Note: presence notifications do not include presence subscriptions,
   only presence information that is broadcasted to the user because the
   user previously subscribed to a contact's presence information.  Thus
   this includes presence stanzas with no 'type' attribute or of
   type='unavailable' only.

   User blocks based on JID:

   <iq type='set' id='presin1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presin-jid-example'>
         <item type='jid' value='tybalt@capulet.com'
               action='deny' order='7'>
           <presence-in/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive presence notifications from the user with the
   specified JID.







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   User blocks based on roster group:

   <iq type='set' id='presin2'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presin-group-example'>
         <item type='group' value='Enemies' action='deny' order='8'>
           <presence-in/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive presence notifications from any users in the
   specified roster group.

   User blocks based on subscription type:

   <iq type='set' id='presin3'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presin-sub-example'>
         <item type='subscription' value='none' action='deny' order='9'>
           <presence-in/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive presence notifications from any users with the
   specified subscription type.

   User blocks globally:

   <iq type='set' id='presin4'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presin-global-example'>
         <item action='deny' order='11'>
           <presence-in/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive presence notifications from any other users.





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8.10 Blocking Outbound Presence Notifications

   Server-side privacy lists enable a user to block outgoing presence
   notifications to other users based on the other user's JID, roster
   group, or subscription status, or globally.  The following examples
   illustrate the required protocol.

   Note: presence notifications do not include presence subscriptions,
   only presence information that is broadcasted to contacts because
   those contacts previously subscribed to the user's presence
   information.  Thus this includes presence stanzas with no 'type'
   attribute or of type='unavailable' only.

   User blocks based on JID:

   <iq type='set' id='presout1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presout-jid-example'>
         <item type='jid' value='tybalt@capulet.com'
               action='deny' order='13'>
           <presence-out/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not send presence notifications to the user with the specified
   JID.

   User blocks based on roster group:

   <iq type='set' id='presout2'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presout-group-example'>
         <item type='group' value='Enemies' action='deny' order='15'>
           <presence-out/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not send presence notifications to any users in the specified
   roster group.






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   User blocks based on subscription type:

   <iq type='set' id='presout3'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presout-sub-example'>
         <item type='subscription' value='none'
               action='deny' order='17'>
           <presence-out/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not send presence notifications to any users with the specified
   subscription type.

   User blocks globally:

   <iq type='set' id='presout4'>
     <query xmlns='jabber:iq:privacy'>
       <list name='presout-global-example'>
         <item action='deny' order='23'>
           <presence-out/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not send presence notifications to any other users.

8.11 Blocking IQs

   Server-side privacy lists enable a user to block incoming IQ requests
   of type "get" or "set" from other users based on the other user's
   JID, roster group, or subscription status, or globally.  The
   following examples illustrate the required protocol.













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   User blocks based on JID:

   <iq type='set' id='iq1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='iq-jid-example'>
         <item type='jid' value='tybalt@capulet.com'
               action='deny' order='29'>
           <iq/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive IQ requests of type "get" or "set" from the user
   with the specified JID.

   User blocks based on roster group:

   <iq type='set' id='iq2'>
     <query xmlns='jabber:iq:privacy'>
       <list name='iq-group-example'>
         <item type='group' value='Enemies' action='deny' order='31'>
           <iq/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive IQ requests of type "get" or "set" from any users in
   the specified roster group.

   User blocks based on subscription type:

   <iq type='set' id='iq3'>
     <query xmlns='jabber:iq:privacy'>
       <list name='iq-sub-example'>
         <item type='subscription' value='none'
               action='deny' order='17'>
           <iq/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive IQ requests of type "get" or "set" from any users



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   with the specified subscription type.

   User blocks globally:

   <iq type='set' id='iq4'>
     <query xmlns='jabber:iq:privacy'>
       <list name='iq-global-example'>
         <item action='deny' order='1'>
           <iq/>
         </item>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive IQ requests of type "get" or "set" from any other
   users.

8.12 Blocking All Communication

   Server-side privacy lists enable a user to block all communications
   from and presence to other users based on the other user's JID,
   roster group, or subscription status, or globally.  The following
   examples illustrate the required protocol.

   User blocks based on JID:

   <iq type='set' id='all1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='all-jid-example'>
         <item type='jid' value='tybalt@capulet.com'
               action='deny' order='23'/>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive any communications from, nor send presence to, the
   user with the specified JID.












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   User blocks based on roster group:

   <iq type='set' id='all2'>
     <query xmlns='jabber:iq:privacy'>
       <list name='all-group-example'>
         <item type='group' value='Enemies' action='deny' order='13'/>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive any communications from, nor send presence to, any
   users in the specified roster group.

   User blocks based on subscription type:

   <iq type='set' id='all3'>
     <query xmlns='jabber:iq:privacy'>
       <list name='all-sub-example'>
         <item type='subscription' value='none'
               action='deny' order='11'/>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive any communications from, nor send presence to, any
   users with the specified subscription type.

   User blocks globally:

   <iq type='set' id='all4'>
     <query xmlns='jabber:iq:privacy'>
       <list name='all-global-example'>
         <item action='deny' order='7'/>
       </list>
     </query>
   </iq>

   As a result of creating and applying the foregoing list, the user
   will not receive any communications from, nor send presence to, any
   other users.

8.13 Blocked Entity Attempts to Communicate with User

   If a blocked entity attempts to send messages or presence
   notifications to the user, the user's server SHOULD silently drop the
   stanza and MUST NOT return an error to the sending entity.



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   If a blocked entity attempts to send an IQ stanza of type "get" or
   "set" to the user, the user's server MUST return to the sending
   entity a <feature-not-implemented/> error of class "recipient" in the
   'urn:ietf:params:xml:ns:xmpp-stanzas' namespace, since this is the
   standard error code sent from a client that does not understand the
   namespace of an IQ get or set.  IQ stanzas of other types SHOULD be
   silently dropped by the server.

   Blocked entity attempts to send IQ get:

   <iq
       type='get'
       to='romeo@montague.net'
       from='tybalt@capulet.com/pda'
       id='probing1'>
     <query xmlns='jabber:iq:version'/>
   </iq>

   Server returns error to blocked entity:

   <iq
       type='error'
       from='romeo@montague.net'
       to='tybalt@capulet.com/pda'
       id='probing1'>
     <query xmlns='jabber:iq:version'/>
     <error class='recipient'>
       <condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
         <feature-not-implemented/>
       </condition>
     </error>
   </iq>


8.14 Higher-Level Heuristics

   When building a representation of a higher-level privacy heuristic, a
   client SHOULD use the simplest possible representation.

   For example, the heuristic "block all communications with any user
   not in my roster" could be constructed in any of the following ways:

   o  accept communications from all JIDs in my roster (i.e., listing
      each JID as a separate list item), but deny communications with
      everyone else

   o  accept communications from any user who is in one of the groups
      that make up my roster (i.e., listing each group as a separate



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      list item), but deny communications from everyone else

   o  accept communications from any user with whom I have a
      subscription of 'both' or 'to' or 'from' (i.e., listing each
      subscription value separately), but deny communications from
      everyone else

   o  deny communications from anyone whose subscription state is 'none'

   The final representation is the simplest and SHOULD be used; here is
   the XML that would be sent in this case:

   <iq type='set' id='heuristic1'>
     <query xmlns='jabber:iq:privacy'>
       <list name='heuristic-example'>
         <item type='subscription' value='none'
               action='deny' order='437'/>
       </list>
     </query>
   </iq>































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9. Routing and Delivery Rules

9.1 Client Generation of To Addresses

   Many XMPP stanzas possess a 'to' address that specifies the intended
   recipient of the stanza.  When a server receives a stanza possessing
   a 'to' attribute from a connected client, it is responsible for
   either directly delivering the stanza to the intended recipient (if
   the recipient is served by the same server) or for routing the stanza
   to another server (if the recipient is not served by the same
   server).  (This does not necessary imply that the recipient is on a
   different domain from the sender, since one server could host
   multiple domains.) If delivery to the intended recipient is
   unsuccessful or the recipient's server cannot be contacted, the
   sender's server is responsible for returning an error to the sender;
   if the recipient's server can be contacted but delivery by the
   recipient's server to the recipient is unsuccessful, the recipient's
   server is responsible for returning an error to the sender by way of
   the sender's server.

   If a client does not specify a 'to' address on a stanza, it is
   implied that the stanza is meant to be handled by the sender's server
   on behalf of the sender.  Although this functionality is normally not
   used in the case of message stanzas, it is quite common with regard
   to both presence and IQ stanzas.  In the case of presence stanzas,
   the user's presence information is normally sent from the client to
   the user's server without a 'to' attribute, and subsequently
   broadcasted to all entities that are subscribed to the sender's
   presence information using a classic publish-subscribe model.  In the
   case of IQ stanzas, requests in many extended namespaces (e.g.,
   jabber:iq:roster) are normally sent from the client to the server
   without a 'to' attribute, and handled by the server on behalf of the
   user (e.g., to manage roster information stored by the server).

   If a user's client would like to request information about the user's
   server itself (e.g., for the purpose of service discovery), it MUST
   include the server's JID in the 'to' address of the IQ request.

9.2 Server Handling of XML Stanzas

   Any appropriate privacy rules (Section 8) SHOULD be applied by the
   server first.  Following the application of any privacy rules, XML
   stanzas that are not handled directly by a server (e.g., for the
   purpose of data storage or rebroadcasting) SHOULD be routed or
   delivered to the intended recipient of the stanza as represented by a
   JID in the 'to' attribute.  The following rules apply:

   o  If the JID contains a resource identifier (to="user@domain/



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      resource"), the stanza MUST be delivered to the resource that
      exactly matches the resource identifier.

   o  If the JID contains a resource identifier and there are no
      matching resources, the server SHOULD return to the sender a
      <recipient-unavailable/> error of class "recipient" in the
      'urn:ietf:params:xml:ns:xmpp-stanzas' namespace.

   o  If the JID contains only a user@domain and there is at least one
      connected resource available for the user, the server SHOULD
      deliver the stanza to an appropriate resource based on the
      availability state, priority, and connect time of the connected
      resource(s).  (For instance, the server MAY deliver the stanza to
      the resource with the highest value for the <priority/> element,
      and decide between resources of equal priority based on most
      recent connect time or most recent activity time; however, all
      such rules are implementation-specific.) However, the server MUST
      NOT deliver the stanza to a resource that provided a negative
      value for the <priority/> element.

   o  If the JID contains only a user@domain and there are no connected
      resources available for the user (e.g., an IM user is offline),
      the server MAY choose to store the stanza on behalf of the user
      and deliver the stanza when a resource becomes available for that
      user.  If offline storage is not enabled, the server MUST return
      to the sender a <service-unavailable/> error of class "server" in
      the 'urn:ietf:params:xml:ns:xmpp-stanzas' namespace.  Note:
      offline storage is not defined in XMPP since it is a matter of
      implementation.






















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10. IANA Considerations

10.1 XML Namespace Name for Session Data

   A URN sub-namespace for session-related data in the Extensible
   Messaging and Presence Protocol (XMPP) is defined as follows.

   URI: urn:ietf:params:xml:ns:xmpp-session

   Specification: [RFCXXXX]

   Description: This is the XML namespace name for session-related data
      in the Extensible Messaging and Presence Protocol (XMPP) as
      defined by [RFCXXXX].

   Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>



































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11. Security Considerations

   For security considerations, refer to the relevant section of XMPP
   Core [1].















































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Normative References

   [1]  Saint-Andre, P. and J. Miller, "XMPP Core (draft-ietf-xmpp-core-
        10, work in progress)", April 2003.

   [2]  Day, M., Aggarwal, S., Mohr, G. and J. Vincent, "A Model for
        Presence and Instant Messaging", RFC 2779, February 2000,
        <http://www.ietf.org/rfc/rfc2779.txt>.

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

   [4]  Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and
        Instant Messaging", RFC 2778, February 2000, <http://
        www.ietf.org/rfc/rfc2778.txt>.




































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Informative References

   [5]  Jabber Software Foundation, "Jabber Software Foundation", August
        2001, <http://www.jabber.org/>.

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


Authors' Addresses

   Peter Saint-Andre
   Jabber Software Foundation

   EMail: stpeter@jabber.org
   URI:   http://www.jabber.org/people/stpeter.php


   Jeremie Miller
   Jabber Software Foundation

   EMail: jeremie@jabber.org
   URI:   http://www.jabber.org/people/jer.php




























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Appendix A. vCards

   Sections 3.1.3 and 4.1.4 of RFC 2779 [2] require that it be possible
   to retrieve non-IM contact information for other users (e.g.,
   telephone number or email address).  An XML representation of the
   vCard specification defined in RFC 2426 [6] is in common use within
   the Jabber community to provide such information.  Documentation of
   this protocol is maintained by the Jabber Software Foundation [5] at
   <http://www.jabber.org/protocol/>.










































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Appendix B. XML Schemas

B.1 session

   <?xml version='1.0' encoding='UTF-8'?>
   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='urn:ietf:params:xml:ns:xmpp-session'
       xmlns='urn:ietf:params:xml:ns:xmpp-session'
       elementFormDefault='qualified'>

     <xs:element name='session'/>

   </xs:schema>


B.2 jabber:iq:last

   <?xml version='1.0' encoding='UTF-8'?>
   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='jabber:iq:last'
       xmlns='jabber:iq:last'
       elementFormDefault='qualified'>

     <xs:element name='query'>
       <xs:complexType>
         <xs:attribute name='seconds' type='xs:unsignedLong'
                       use='optional'/>
       </xs:complexType>
     </xs:element>

   </xs:schema>


B.3 jabber:iq:privacy

   <?xml version='1.0' encoding='UTF-8'?>
   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='jabber:iq:privacy'
       xmlns='jabber:iq:privacy'
       elementFormDefault='qualified'>

     <xs:element name='query'>
       <xs:complexType>
         <xs:sequence>
           <xs:element ref='active' minOccurs='0' maxOccurs='1'/>



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           <xs:element ref='default' minOccurs='0' maxOccurs='1'/>
           <xs:element ref='list' minOccurs='0' maxOccurs='unbounded'/>
         </xs:sequence>
       </xs:complexType>
     </xs:element>

     <xs:element name='active'>
       <xs:complexType>
         <xs:attribute name='name' type='xs:string' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='default'>
       <xs:complexType>
         <xs:attribute name='name' type='xs:string' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='list'>
       <xs:complexType>
         <xs:choice minOccurs='0' maxOccurs='unbounded'>
           <xs:element ref='item' minOccurs='0' maxOccurs='unbounded'/>
         </xs:choice>
         <xs:attribute name='name' type='xs:string' use='required'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='item'>
       <xs:complexType>
         <xs:sequence>
           <xs:element ref='iq' minOccurs='0' maxOccurs='1'/>
           <xs:element ref='message' minOccurs='0' maxOccurs='1'/>
           <xs:element ref='presence-in' minOccurs='0' maxOccurs='1'/>
           <xs:element ref='presence-out' minOccurs='0' maxOccurs='1'/>
         </xs:sequence>
         <xs:attribute name='action' use='required'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>
               <xs:enumeration value='allow'/>
               <xs:enumeration value='deny'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute name='order' type='xs:nonNegativeInteger'
                       use='required'/>
         <xs:attribute name='type' use='optional'>
           <xs:simpleType>
             <xs:restriction base='xs:NCName'>



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               <xs:enumeration value='group'/>
               <xs:enumeration value='jid'/>
               <xs:enumeration value='subscription'/>
             </xs:restriction>
           </xs:simpleType>
         </xs:attribute>
         <xs:attribute name='value' type='xs:string' use='optional'/>
       </xs:complexType>
     </xs:element>

     <xs:element name='iq'/>
     <xs:element name='message'/>
     <xs:element name='presence-in'/>
     <xs:element name='presence-out'/>

   </xs:schema>


B.4 jabber:iq:privacy:error

   <?xml version='1.0' encoding='UTF-8'?>
   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='jabber:iq:privacy:error'
       xmlns='jabber:iq:privacy:error'
       elementFormDefault='qualified'>

     <xs:element name='condition'>
       <xs:complexType>
         <xs:choice maxOccurs='1'>
           <xs:element ref='list-not-found'/>
           <xs:element ref='too-many-lists'/>
         </xs:choice>
       </xs:complexType>
     </xs:element>

     <xs:element name='list-not-found' type='xs:string'/>
     <xs:element name='too-many-lists' type='xs:string'/>

   </xs:schema>


B.5 jabber:iq:roster

   <?xml version='1.0' encoding='UTF-8'?>
   <xs:schema
       xmlns:xs='http://www.w3.org/2001/XMLSchema'
       targetNamespace='http://www.jabber.org/protocol'



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       xmlns='http://www.jabber.org/protocol'
       elementFormDefault='qualified'>

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

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

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

   </xs:schema>









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Appendix C. Revision History

   Note to RFC Editor: please remove this entire appendix, and the
   corresponding entries in the table of contents, prior to publication.

C.1 Changes from draft-ietf-xmpp-im-08

   o  Removed authorization content (now addressed in XMPP Core).

   o  Added protocol for initiating an IM session, including schema and
      IANA registration template.

   o  Corrected <*-condition/> elements to be <condition/>.

   o  Made small editorial changes to address RFC Editor requirements.


C.2 Changes from draft-ietf-xmpp-im-07

   o  Added several error cases for resource authorization and updated
      relevant schema.


C.3 Changes from draft-ietf-xmpp-im-06

   o  Specified that IQ result stanzas are required in response to
      roster pushes.

   o  Changed stanza error namespace names to conform to the format
      defined in "The IETF XML Registry" as specified in XMPP Core.

   o  Removed note to RFC Editor regarding provisional namespace names.


C.4 Changes from draft-ietf-xmpp-im-05

   o  Removed use of ask='unsubscribe' per list discussion.

   o  Clarified handling of resource conflict during authorization.

   o  Added schemas for jabber:iq:auth, jabber:iq:auth:error, and
      jabber:iq:privacy:error.

   o  Corrected several small protocol errors in the examples.

   o  Clarified semantics of message types.





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C.5 Changes from draft-ietf-xmpp-im-04

   o  Specified sending of unavailable presence after unsubscribe and
      subscription-cancellation actions.

   o  Further specified syntax and business rules for privacy lists.

   o  Brought error codes into line with definitions in draft-ietf-xmpp-
      core.

   o  Added note to RFC Editor regarding provisional namespace names.

   o  Removed vCard content and DTD, instead pointing to JSF
      documentation.


C.6 Changes from draft-ietf-xmpp-im-03

   o  Fixed order processing on privacy rules per list discussion.

   o  Made numerous small editorial changes.


C.7 Changes from draft-ietf-xmpp-im-02

   o  Added a great deal more detail to the narrative regarding server-
      side privacy rules as well as the interaction between rosters and
      subscriptions.

   o  Removed DTDs in favor of schemas (with the exception of vCard
      XML).

   o  Removed non-normative documentation of authentication using
      jabber:iq:auth and of in-band registration using
      jabber:iq:register, since these are maintained by the Jabber
      Software Foundation and are not part of the XMPP specification.


C.8 Changes from draft-ietf-xmpp-im-01

   o  Made numerous small editorial changes.


C.9 Changes from draft-ietf-xmpp-im-00

   o  Moved registration and authentication via jabber:iq:auth to non-
      normative appendices.




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   o  Changed initial presence stanza from MUST be empty to SHOULD be
      empty.

   o  Specified that user or clients should not send presence stanzas of
      type 'probe'.

   o  Specified the algorithm for digest passwords.


C.10 Changes from draft-miller-xmpp-im-02

   o  Added information about the 'jabber:iq:last' protocol to meet the
      requirement defined in section 3.2.4 of RFC 2779.

   o  Added information about the 'jabber:iq:privacy' protocol to meet
      the requirement defined in section 2.3.5 of RFC 2779.

   o  Added information about the vCard XML protocol to meet the
      requirement defined in sections 3.1.3 and 4.1.4 of RFC 2779.

   o  Changed the material describing authentication (but not resource
      authorization) with 'jabber:iq:auth' to non-normative.

   o  Noted that the only watchers are subscribers.

   o  Nomenclature changes: (1) from "chunks" to "stanzas"; (2) from
      "host" to "server"; (3) from "node" to "client" or "user" (as
      appropriate).























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Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
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   kind, provided that the above copyright notice and this paragraph are
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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