Network Working Group                                P. Saint-Andre, Ed.
Request for Comments: 3921                    Jabber Software Foundation
Category: Standards Track                                   October 2004


         Extensible Messaging and Presence Protocol (XMPP):
                    Instant Messaging and Presence

Status of this Memo

  This document specifies an Internet standards track protocol for the
  Internet community, and requests discussion and suggestions for
  improvements.  Please refer to the current edition of the "Internet
  Official Protocol Standards" (STD 1) for the standardization state
  and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (2004).

Abstract

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

























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Table of Contents

  1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   2
  2.   Syntax of XML Stanzas  . . . . . . . . . . . . . . . . . . .   4
  3.   Session Establishment  . . . . . . . . . . . . . . . . . . .  10
  4.   Exchanging Messages  . . . . . . . . . . . . . . . . . . . .  13
  5.   Exchanging Presence Information  . . . . . . . . . . . . . .  16
  6.   Managing Subscriptions . . . . . . . . . . . . . . . . . . .  26
  7.   Roster Management  . . . . . . . . . . . . . . . . . . . . .  27
  8.   Integration of Roster Items and Presence Subscriptions . . .  32
  9.   Subscription States  . . . . . . . . . . . . . . . . . . . .  56
  10.  Blocking Communication . . . . . . . . . . . . . . . . . . .  62
  11.  Server Rules for Handling XML Stanzas  . . . . . . . . . . .  85
  12.  IM and Presence Compliance Requirements  . . . . . . . . . .  88
  13.  Internationalization Considerations  . . . . . . . . . . . .  89
  14.  Security Considerations  . . . . . . . . . . . . . . . . . .  89
  15.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .  90
  16.  References . . . . . . . . . . . . . . . . . . . . . . . . .  91
  A.   vCards . . . . . . . . . . . . . . . . . . . . . . . . . . .  93
  B.   XML Schemas. . . . . . . . . . . . . . . . . . . . . . . . .  93
  C.   Differences Between Jabber IM/Presence Protocols and XMPP. . 105
  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . .  106
  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . .  106
  Author's Address. . . . . . . . . . . . . . . . . . . . . . . . . 106
  Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 107

1.  Introduction

1.1.  Overview

  The Extensible Messaging and Presence Protocol (XMPP) is a protocol
  for streaming XML [XML] elements in order to exchange messages and
  presence information in close to real time.  The core features of
  XMPP are defined in Extensible Messaging and Presence Protocol
  (XMPP): Core [XMPP-CORE].  These features -- mainly XML streams, use
  of TLS and SASL, and the <message/>, <presence/>, and <iq/> children
  of the stream root -- provide the building blocks for many types of
  near-real-time applications, which may be layered on top of the core
  by sending application-specific data qualified by particular XML
  namespaces [XML-NAMES].  This memo describes extensions to and
  applications of the core features of XMPP that provide the basic
  functionality expected of an instant messaging (IM) and presence
  application as defined in RFC 2779 [IMP-REQS].








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1.2.  Requirements

  For the purposes of this memo, the requirements of a basic instant
  messaging and presence application are defined by [IMP-REQS], which
  at a high level stipulates that a user must be able to complete the
  following use cases:

  o  Exchange messages with other users
  o  Exchange presence information with other users
  o  Manage subscriptions to and from other users
  o  Manage items in a contact list (in XMPP this is called a "roster")
  o  Block communications to or from specific other users

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

  [IMP-REQS] also stipulates that presence services must be separable
  from instant messaging services; i.e., it must be possible to use the
  protocol to provide a presence service, an instant messaging service,
  or both.  Although the text of this memo assumes that implementations
  and deployments will want to offer a unified instant messaging and
  presence service, there is no requirement that a service must offer
  both a presence service and an instant messaging service, and the
  protocol makes it possible to offer separate and distinct services
  for presence and for instant messaging.

  Note: While XMPP-based instant messaging and presence meets the
  requirements of [IMP-REQS], it was not designed explicitly with that
  specification in mind, since the base protocol evolved through an
  open development process within the Jabber open-source community
  before RFC 2779 was written.  Note also that although protocols
  addressing many other functionality areas have been defined in the
  Jabber community, such protocols are not included in this memo
  because they are not required by [IMP-REQS].

1.3.  Terminology

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

  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 BCP
  14, RFC 2119 [TERMS].







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2.  Syntax of XML Stanzas

  The basic semantics and common attributes of XML stanzas qualified by
  the 'jabber:client' and 'jabber:server' namespaces are defined in
  [XMPP-CORE].  However, these namespaces also define various child
  elements, as well as values for the common 'type' attribute, that are
  specific to instant messaging and presence applications.  Thus,
  before addressing particular "use cases" for such applications, we
  here further describe the syntax of XML stanzas, thereby
  supplementing the discussion in [XMPP-CORE].

2.1.  Message Syntax

  Message stanzas qualified by the 'jabber:client' or 'jabber:server'
  namespace are used to "push" information to another entity.  Common
  uses in instant messaging applications include single messages,
  messages sent in the context of a chat conversation, messages sent in
  the context of a multi-user chat room, headlines and other alerts,
  and errors.

2.1.1.  Types of Message

  The 'type' attribute of a message stanza is RECOMMENDED; if included,
  it specifies the conversational context of the message, thus
  providing a hint regarding presentation (e.g., in a GUI).  If
  included, the 'type' attribute MUST have one of the following values:

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

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

  o  groupchat -- The message is sent in the context of a multi-user
     chat environment (similar to that of [IRC]).  A compliant client
     SHOULD present the message in an interface enabling many-to-many
     chat between the parties, including a roster of parties in the
     chatroom and an appropriate conversation history.  Full definition
     of XMPP-based groupchat protocols is out of scope for this memo.

  o  headline -- The message is probably generated by an automated
     service that delivers or broadcasts content (news, sports, market
     information, RSS feeds, etc.).  No reply to the message is
     expected, and a compliant client SHOULD present the message in an



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     interface that appropriately differentiates the message from
     standalone messages, chat sessions, or groupchat sessions (e.g.,
     by not providing the recipient with the ability to reply).

  o  normal -- The message is a single message that is sent outside the
     context of a one-to-one conversation or groupchat, and to which it
     is expected that the recipient will reply.  A compliant client
     SHOULD present the message in an interface enabling the recipient
     to reply, but without a conversation history.

  An IM application SHOULD support all of the foregoing message types;
  if an application receives a message with no 'type' attribute or the
  application does not understand the value of the 'type' attribute
  provided, it MUST consider the message to be of type "normal" (i.e.,
  "normal" is the default).  The "error" type MUST be generated only in
  response to an error related to a message received from another
  entity.

  Although the 'type' attribute is 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').

2.1.2.  Child Elements

  As described under extended namespaces (Section 2.4), a message
  stanza MAY contain any properly-namespaced child element.

  In accordance with the default namespace declaration, by default a
  message stanza is qualified by the 'jabber:client' or 'jabber:server'
  namespace, which defines certain allowable children of message
  stanzas.  If the message stanza is of type "error", it MUST include
  an <error/> child; for details, see [XMPP-CORE].  Otherwise, the
  message stanza MAY contain any of the following child elements
  without an explicit namespace declaration:

  1.  <subject/>
  2.  <body/>
  3.  <thread/>

2.1.2.1.  Subject

  The <subject/> element contains human-readable XML character data
  that specifies the topic of the message.  The <subject/> element MUST
  NOT possess any attributes, with the exception of the 'xml:lang'
  attribute.  Multiple instances of the <subject/> element MAY be
  included for the purpose of providing alternate versions of the same



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  subject, but only if each instance possesses an 'xml:lang' attribute
  with a distinct language value.  The <subject/> element MUST NOT
  contain mixed content (as defined in Section 3.2.2 of [XML]).

2.1.2.2.  Body

  The <body/> element contains human-readable XML character data that
  specifies the textual contents of the message; this child element is
  normally included but is OPTIONAL.  The <body/> element MUST NOT
  possess any attributes, with the exception of the 'xml:lang'
  attribute.  Multiple instances of the <body/> element MAY be included
  but only if each instance possesses an 'xml:lang' attribute with a
  distinct language value.  The <body/> element MUST NOT contain mixed
  content (as defined in Section 3.2.2 of [XML]).

2.1.2.3.  Thread

  The <thread/> element contains non-human-readable XML character data
  specifying an identifier that is used for tracking a conversation
  thread (sometimes referred to as an "instant messaging session")
  between two entities.  The value of the <thread/> element is
  generated by the sender and SHOULD be copied back in any replies.  If
  used, it MUST be unique to that conversation thread within the stream
  and MUST be consistent throughout that conversation (a client that
  receives a message from the same full JID but with a different thread
  ID MUST assume that the message in question exists outside the
  context of the existing conversation thread).  The use of the
  <thread/> element is OPTIONAL and is not used to identify individual
  messages, only conversations.  A message stanza MUST NOT contain more
  than one <thread/> element.  The <thread/> element MUST NOT possess
  any attributes.  The value of the <thread/> element MUST be treated
  as opaque by entities; no semantic meaning may be derived from it,
  and only exact comparisons may be made against it.  The <thread/>
  element MUST NOT contain mixed content (as defined in Section 3.2.2
  of [XML]).

2.2.  Presence Syntax

  Presence stanzas are used qualified by the 'jabber:client' or
  'jabber:server' namespace to express an entity's current network
  availability (offline or online, along with various sub-states of the
  latter and optional user-defined descriptive text), and to notify
  other entities of that availability.  Presence stanzas are also used
  to negotiate and manage subscriptions to the presence of other
  entities.






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2.2.1.  Types of Presence

  The 'type' attribute of a presence stanza is OPTIONAL.  A presence
  stanza that does not possess a 'type' attribute is used to signal to
  the server that the sender is online and available for communication.
  If included, the 'type' attribute specifies a lack of availability, a
  request to manage a subscription to another entity's presence, a
  request for another entity's current presence, or an error related to
  a previously-sent presence stanza.  If included, the 'type' attribute
  MUST have one of the following values:

  o  unavailable -- Signals that the entity is no longer available for
     communication.

  o  subscribe -- The sender wishes to subscribe to the recipient's
     presence.

  o  subscribed -- The sender has allowed the recipient to receive
     their presence.

  o  unsubscribe -- The sender is unsubscribing from another entity's
     presence.

  o  unsubscribed -- The subscription request has been denied or a
     previously-granted subscription has been cancelled.

  o  probe -- A request for an entity's current presence; SHOULD be
     generated only by a server on behalf of a user.

  o  error -- An error has occurred regarding processing or delivery of
     a previously-sent presence stanza.

  For detailed information regarding presence semantics and the
  subscription model used in the context of XMPP-based instant
  messaging and presence applications, refer to Exchanging Presence
  Information (Section 5) and Managing Subscriptions (Section 6).

2.2.2.  Child Elements

  As described under extended namespaces (Section 2.4), a presence
  stanza MAY contain any properly-namespaced child element.

  In accordance with the default namespace declaration, by default a
  presence stanza is qualified by the 'jabber:client' or
  'jabber:server' namespace, which defines certain allowable children
  of presence stanzas.  If the presence stanza is of type "error", it
  MUST include an <error/> child; for details, see [XMPP-CORE].  If the
  presence stanza possesses no 'type' attribute, it MAY contain any of



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  the following child elements (note that the <status/> child MAY be
  sent in a presence stanza of type "unavailable" or, for historical
  reasons, "subscribe"):

  1.  <show/>
  2.  <status/>
  3.  <priority/>

2.2.2.1.  Show

  The OPTIONAL <show/> element contains non-human-readable XML
  character data that specifies the particular availability status of
  an entity or specific resource.  A presence stanza MUST NOT contain
  more than one <show/> element.  The <show/> element MUST NOT possess
  any attributes.  If provided, the XML character data value MUST be
  one of the following (additional availability types could be defined
  through a properly-namespaced child element of the presence stanza):

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

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

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

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

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

2.2.2.2.  Status

  The OPTIONAL <status/> element contains XML character data specifying
  a natural-language description of availability status.  It is
  normally used in conjunction with the show element to provide a
  detailed description of an availability state (e.g., "In a meeting").
  The <status/> element MUST NOT possess any attributes, with the
  exception of the 'xml:lang' attribute.  Multiple instances of the
  <status/> element MAY be included but only if each instance possesses
  an 'xml:lang' attribute with a distinct language value.

2.2.2.3.  Priority

  The OPTIONAL <priority/> element contains non-human-readable XML
  character data that specifies the priority level of the resource. The
  value MUST be an integer between -128 and +127.  A presence stanza
  MUST NOT contain more than one <priority/> element.  The <priority/>
  element MUST NOT possess any attributes.  If no priority is provided,



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  a server SHOULD consider the priority to be zero.  For information
  regarding the semantics of priority values in stanza routing within
  instant messaging and presence applications, refer to Server Rules
  for Handling XML Stanzas (Section 11).

2.3.  IQ Syntax

  IQ stanzas provide a structured request-response mechanism.  The
  basic semantics of that mechanism (e.g., that the 'id' attribute is
  REQUIRED) are defined in [XMPP-CORE], whereas the specific semantics
  required to complete particular use cases are defined in all cases by
  an extended namespace (Section 2.4) (note that the 'jabber:client'
  and 'jabber:server' namespaces do not define any children of IQ
  stanzas other than the common <error/>).  This memo defines two such
  extended namespaces, one for Roster Management (Section 7) and the
  other for Blocking Communication (Section 10); however, an IQ stanza
  MAY contain structured information qualified by any extended
  namespace.

2.4.  Extended Namespaces

  While the three XML stanza kinds defined in the "jabber:client" or
  "jabber:server" namespace (along with their attributes and child
  elements) provide a basic level of functionality for messaging and
  presence, XMPP uses XML namespaces to extend the stanzas for the
  purpose of providing additional functionality.  Thus a message or
  presence stanza MAY contain one or more optional child elements
  specifying content that extends the meaning of the message (e.g., an
  XHTML-formatted version of the message body), and an IQ stanza MAY
  contain one such child element.  This child element MAY have any name
  and MUST possess an 'xmlns' namespace declaration (other than
  "jabber:client", "jabber:server", or
  "http://etherx.jabber.org/streams") that defines all data contained
  within the child element.

  Support for any given extended namespace is OPTIONAL on the part of
  any implementation (aside from the extended namespaces defined
  herein).  If an entity does not understand such a namespace, the
  entity's expected behavior depends on whether the entity is (1) the
  recipient or (2) an entity that is routing the stanza to the
  recipient:

  Recipient: If a recipient receives a stanza that contains a child
     element it does not understand, it SHOULD ignore that specific XML
     data, i.e., it SHOULD not process it or present it to a user or
     associated application (if any).  In particular:





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     *  If an entity receives a message or presence stanza that
        contains XML data qualified by a namespace it does not
        understand, the portion of the stanza that is in the unknown
        namespace SHOULD be ignored.

     *  If an entity receives a message stanza whose only child element
        is qualified by a namespace it does not understand, it MUST
        ignore the entire stanza.

     *  If an entity receives an IQ stanza of type "get" or "set"
        containing a child element qualified by a namespace it does not
        understand, the entity SHOULD return an IQ stanza of type
        "error" with an error condition of <service-unavailable/>.

  Router: If a routing entity (usually a server) handles a stanza that
     contains a child element it does not understand, it SHOULD ignore
     the associated XML data by passing it on untouched to the
     recipient.

3.  Session Establishment

  Most instant messaging and presence applications based on XMPP are
  implemented via a client-server architecture that requires a client
  to establish a session on a server in order to engage in the expected
  instant messaging and presence activities.  However, there are
  several pre-conditions that MUST be met before a client can establish
  an instant messaging and presence session.  These are:

  1.  Stream Authentication -- a client MUST complete stream
      authentication as documented in [XMPP-CORE] before attempting to
      establish a session or send any XML stanzas.
  2.  Resource Binding -- after completing stream authentication, a
      client MUST bind a resource to the stream so that the client's
      address is of the form <user@domain/resource>, after which the
      entity is now said to be a "connected resource" in the
      terminology of [XMPP-CORE].

  If a server supports sessions, it MUST include a <session/> element
  qualified by the 'urn:ietf:params:xml:ns:xmpp-session' namespace in
  the stream features it advertises to a client after the completion of
  stream authentication as defined in [XMPP-CORE]:










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  Server advertises session establishment feature to client:

  <stream:stream
      xmlns='jabber:client'
      xmlns:stream='http://etherx.jabber.org/streams'
      id='c2s_345'
      from='example.com'
      version='1.0'>
  <stream:features>
    <bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/>
    <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
  </stream:features>

  Upon being so informed that session establishment is required (and
  after completing resource binding), the client MUST establish a
  session if it desires to engage in instant messaging and presence
  functionality; it completes this step by sending to the server an IQ
  stanza of type "set" containing an empty <session/> child element
  qualified by the 'urn:ietf:params:xml:ns:xmpp-session' namespace:

  Step 1: Client requests session with server:

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

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

  <iq from='example.com'
      type='result'
      id='sess_1'/>

  Upon establishing a session, a connected resource (in the terminology
  of [XMPP-CORE]) is said to be an "active resource".

  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 resource
  associated with a resource identifier 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 from='example.com' type='error' id='sess_1'>
    <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
    <error type='wait'>
      <internal-server-error
          xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    </error>
  </iq>

  If the username or resource is not allowed to create a session, the
  server MUST return an error (e.g., forbidden).

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

  <iq from='example.com' type='error' id='sess_1'>
    <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
    <error type='auth'>
      <forbidden
          xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    </error>
  </iq>

  If there is already an active resource of the same name, the server
  MUST either (1) terminate the active resource and allow the
  newly-requested session, or (2) disallow the newly-requested session
  and maintain the active resource.  Which of these the server does is
  up to the implementation, although it is RECOMMENDED to implement
  case #1.  In case #1, the server SHOULD send a <conflict/> stream
  error to the active resource, terminate the XML stream and underlying
  TCP connection for the active resource, and return a IQ stanza of
  type "result" (indicating success) to the newly-requested session. In
  case #2, the server SHOULD send a <conflict/> stanza error to the
  newly-requested session but maintain the XML stream for that
  connection so that the newly-requested session has an opportunity to
  negotiate a non-conflicting resource identifier before sending
  another request for session establishment.

  Step 2 (alt): Server informs existing active resource of resource
  conflict (case #1):

  <stream:error>
    <conflict xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
  </stream:error>
  </stream:stream>





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  Step 2 (alt): Server informs newly-requested session of resource
  conflict (case #2):

  <iq from='example.com' type='error' id='sess_1'>
    <session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
    <error type='cancel'>
      <conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    </error>
  </iq>

  After establishing a session, a client SHOULD send initial presence
  and request its roster as described below, although these actions are
  OPTIONAL.

  Note: Before allowing the creation of instant messaging and presence
  sessions, a server MAY require prior account provisioning.  Possible
  methods for account provisioning include account creation by a server
  administrator as well as in-band account registration using the
  'jabber:iq:register' namespace; the latter method is out of scope for
  this memo, but is documented in [JEP-0077], published by the Jabber
  Software Foundation [JSF].

4.  Exchanging Messages

  Exchanging messages is a basic use of XMPP and is brought about when
  a user generates a message stanza that is addressed to another
  entity.  As defined under Server Rules for Handling XML Stanzas
  (Section 11), the sender's server is responsible for delivering the
  message to the intended recipient (if the recipient is on the same
  server) or for routing the message to the recipient's server (if the
  recipient is on a different server).

  For information regarding the syntax of message stanzas as well as
  their defined attributes and child elements, refer to Message Syntax
  (Section 2.1).

4.1.  Specifying an Intended Recipient

  An instant messaging client SHOULD specify an intended recipient for
  a message by providing the JID of an entity other than the sender in
  the 'to' attribute of the <message/> stanza.  If the message is being
  sent in reply to a message previously received from an address of the
  form <user@domain/resource> (e.g., within the context of a chat
  session), the value of the 'to' address SHOULD be of the form
  <user@domain/resource> rather than of the form <user@domain> unless
  the sender has knowledge (via presence) that the intended recipient's
  resource is no longer available.  If the message is being sent




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

4.2.  Specifying a Message Type

  As noted, it is RECOMMENDED for a message stanza to possess a 'type'
  attribute whose value captures the conversational context (if any) of
  the message (see Type (Section 2.1.1)).

  The following example shows a valid value of the 'type' attribute:

  Example: A message of a defined type:

  <message
      to='[email protected]'
      from='[email protected]/balcony'
      type='chat'
      xml:lang='en'>
    <body>Wherefore art thou, Romeo?</body>
  </message>

4.3.  Specifying a Message Body

  A message stanza MAY (and often will) contain a child <body/> element
  whose XML character data specifies the primary meaning of the message
  (see Body (Section 2.1.2.2)).

  Example: A message with a body:

  <message
      to='[email protected]'
      from='[email protected]/balcony'
      type='chat'
      xml:lang='en'>
    <body>Wherefore art thou, Romeo?</body>
    <body xml:lang='cz'>Pro&#x010D;e&#x017D; jsi ty, Romeo?</body>
  </message>

4.4.  Specifying a Message Subject

  A message stanza MAY contain one or more child <subject/> elements
  specifying the topic of the message (see Subject (Section 2.1.2.1)).








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  Example: A message with a subject:

  <message
      to='[email protected]'
      from='[email protected]/balcony'
      type='chat'
      xml:lang='en'>
    <subject>I implore you!</subject>
    <subject
        xml:lang='cz'>&#x00DA;p&#x011B;nliv&#x011B; prosim!</subject>
    <body>Wherefore art thou, Romeo?</body>
    <body xml:lang='cz'>Pro&#x010D;e&#x017D; jsi ty, Romeo?</body>
  </message>

4.5.  Specifying a Conversation Thread

  A message stanza MAY contain a child <thread/> element specifying the
  conversation thread in which the message is situated, for the purpose
  of tracking the conversation (see Thread (Section 2.1.2.3)).

  Example: A threaded conversation:

  <message
      to='[email protected]/orchard'
      from='[email protected]/balcony'
      type='chat'
      xml:lang='en'>
    <body>Art thou not Romeo, and a Montague?</body>
    <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
  </message>

  <message
      to='[email protected]/balcony'
      from='[email protected]/orchard'
      type='chat'
      xml:lang='en'>
    <body>Neither, fair saint, if either thee dislike.</body>
    <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
  </message>

  <message
      to='[email protected]/orchard'
      from='[email protected]/balcony'
      type='chat'
      xml:lang='en'>
    <body>How cam'st thou hither, tell me, and wherefore?</body>
    <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
  </message>



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5.  Exchanging Presence Information

  Exchanging presence information is made relatively straightforward
  within XMPP by using presence stanzas.  However, we see here a
  contrast to the handling of messages: although a client MAY send
  directed presence information to another entity by including a 'to'
  address, normally presence notifications (i.e., presence stanzas with
  no 'type' or of type "unavailable" and with no 'to' address) are sent
  from a client to its server and then broadcasted by the server to any
  entities that are subscribed to the presence of the sending entity
  (in the terminology of RFC 2778 [IMP-MODEL], these entities are
  subscribers).  This broadcast model does not apply to
  subscription-related presence stanzas or presence stanzas of type
  "error", but to presence notifications only as defined above.  (Note:
  While presence information MAY be provided on a user's behalf by an
  automated service, normally it is provided by the user's client.)

  For information regarding the syntax of presence stanzas as well as
  their defined attributes and child elements, refer to [XMPP-CORE].

5.1.  Client and Server Presence Responsibilities

5.1.1.  Initial Presence

  After establishing a session, a client SHOULD send initial presence
  to the server in order to signal its availability for communications.
  As defined herein, the initial presence stanza (1) MUST possess no
  'to' address (signalling that it is meant to be broadcasted by the
  server on behalf of the client) and (2) MUST possess no 'type'
  attribute (signalling the user's availability).  After sending
  initial presence, an active resource is said to be an "available
  resource".

  Upon receiving initial presence from a client, the user's server MUST
  do the following if there is not already one or more available
  resources for the user (if there is already one or more available
  resources for the user, the server obviously does not need to send
  the presence probes, since it already possesses the requisite
  information):

  1.  Send presence probes (i.e., presence stanzas whose 'type'
      attribute is set to a value of "probe") from the full JID (e.g.,
      <[email protected]/resource>) of the user to all contacts to which
      the user is subscribed in order to determine if they are
      available; such contacts are those for which a JID is present in
      the user's roster with the 'subscription' attribute set to a
      value of "to" or "both".  (Note: The user's server MUST NOT send
      presence probes to contacts from which the user is blocking



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      inbound presence notifications, as described under Blocking
      Inbound Presence Notifications (Section 10.10).)

  2.  Broadcast initial presence from the full JID (e.g.,
      <[email protected]/resource>) of the user to all contacts that are
      subscribed to the user's presence information; such contacts are
      those for which a JID is present in the user's roster with the
      'subscription' attribute set to a value of "from" or "both".
      (Note: The user's server MUST NOT broadcast initial presence to
      contacts to which the user is blocking outbound presence
      notifications, as described under Blocking Outbound Presence
      Notifications (Section 10.11).)

  In addition, the user's server MUST broadcast initial presence from
  the user's new available resource to any of the user's existing
  available resources (if any).

  Upon receiving initial presence from the user, the contact's server
  MUST deliver the user's presence stanza to the full JIDs
  (<[email protected]/resource>) associated with all of the contact's
  available resources, but only if the user is in the contact's roster
  with a subscription state of "to" or "both" and the contact has not
  blocked inbound presence notifications from the user's bare or full
  JID (as defined under Blocking Inbound Presence Notifications
  (Section 10.10)).

  If the user's server receives a presence stanza of type "error" in
  response to the initial presence that it sent to a contact on behalf
  of the user, it SHOULD NOT send further presence updates to that
  contact (until and unless it receives a presence stanza from the
  contact).

5.1.2.  Presence Broadcast

  After sending initial presence, the user MAY update its presence
  information for broadcasting at any time during its session by
  sending a presence stanza with no 'to' address and either no 'type'
  attribute or a 'type' attribute with a value of "unavailable". (Note:
  A user's client SHOULD NOT send a presence update to broadcast
  information that changes independently of the user's presence and
  availability.)

  If the presence stanza lacks a 'type' attribute (i.e., expresses
  availability), the user's server MUST broadcast the full XML of that
  presence stanza to all contacts (1) that are in the user's roster
  with a subscription type of "from" or "both", (2) to whom the user





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  has not blocked outbound presence notifications, and (3) from whom
  the server has not received a presence error during the user's
  session (as well as to any of the user's other available resources).

  If the presence stanza has a 'type' attribute set to a value of
  "unavailable", the user's server MUST broadcast the full XML of that
  presence stanza to all entities that fit the above description, as
  well as to any entities to which the user has sent directed available
  presence during the user's session (if the user has not yet sent
  directed unavailable presence to that entity).

5.1.3.  Presence Probes

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

  1.  If the user is not in the contact's roster with a subscription
      state of "From", "From + Pending Out", or "Both" (as defined
      under Subscription States (Section 9)), the contact's server MUST
      return a presence stanza of type "error" in response to the
      presence probe (however, if a server receives a presence probe
      from a subdomain of the server's hostname or another such trusted
      service, it MAY provide presence information about the user to
      that entity).  Specifically:

      *  if the user is in the contact's roster with a subscription
         state of "None", "None + Pending Out", or "To" (or is not in
         the contact's roster at all), the contact's server MUST return
         a <forbidden/> stanza error in response to the presence probe.

      *  if the user is in the contact's roster with a subscription
         state of "None + Pending In", "None + Pending Out/In", or "To
         + Pending In", the contact's server MUST return a
         <not-authorized/> stanza error in response to the presence
         probe.

  2.  Else, if the contact is blocking presence notifications to the
      user's bare JID or full JID (using either a default list or
      active list as defined under Blocking Outbound Presence
      Notifications (Section 10.11)), the server MUST NOT reply to the
      presence probe.

  3.  Else, if the contact has no available resources, the server MUST
      either (1) reply to the presence probe by sending to the user the
      full XML of the last presence stanza of type "unavailable"
      received by the server from the contact, or (2) not reply at all.





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  4.  Else, if the contact has at least one available resource, the
      server MUST reply to the presence probe by sending to the user
      the full XML of the last presence stanza with no 'to' attribute
      received by the server from each of the contact's available
      resources (again, subject to privacy lists in force for each
      session).

5.1.4.  Directed Presence

  A user MAY send directed presence to another entity (i.e., a presence
  stanza with a 'to' attribute whose value is the JID of the other
  entity and with either no 'type' attribute or a 'type' attribute
  whose value is "unavailable").  There are three possible cases:

  1.  If the user sends directed presence to a contact that is in the
      user's roster with a subscription type of "from" or "both" after
      having sent initial presence and before sending unavailable
      presence broadcast, the user's server MUST route or deliver the
      full XML of that presence stanza (subject to privacy lists) but
      SHOULD NOT otherwise modify the contact's status regarding
      presence broadcast (i.e., it SHOULD include the contact's JID in
      any subsequent presence broadcasts initiated by the user).

  2.  If the user sends directed presence to an entity that is not in
      the user's roster with a subscription type of "from" or "both"
      after having sent initial presence and before sending unavailable
      presence broadcast, the user's server MUST route or deliver the
      full XML of that presence stanza to the entity but MUST NOT
      modify the contact's status regarding available presence
      broadcast (i.e., it MUST NOT include the entity's JID in any
      subsequent broadcasts of available presence initiated by the
      user); however, if the available resource from which the user
      sent the directed presence become unavailable, the user's server
      MUST broadcast that unavailable presence to the entity (if the
      user has not yet sent directed unavailable presence to that
      entity).

  3.  If the user sends directed presence without first sending initial
      presence or after having sent unavailable presence broadcast
      (i.e., the resource is active but not available), the user's
      server MUST treat the entities to which the user sends directed
      presence in the same way that it treats the entities listed in
      case #2 above.








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5.1.5.  Unavailable Presence

  Before ending its session with a server, a client SHOULD gracefully
  become unavailable by sending a final presence stanza that possesses
  no 'to' attribute and that possesses a 'type' attribute whose value
  is "unavailable" (optionally, the final presence stanza MAY contain
  one or more <status/> elements specifying the reason why the user is
  no longer available).  However, the user's server MUST NOT depend on
  receiving final presence from an available resource, since the
  resource may become unavailable unexpectedly or may be timed out by
  the server.  If one of the user's resources becomes unavailable for
  any reason (either gracefully or ungracefully), the user's server
  MUST broadcast unavailable presence to all contacts (1) that are in
  the user's roster with a subscription type of "from" or "both", (2)
  to whom the user has not blocked outbound presence, and (3) from whom
  the server has not received a presence error during the user's
  session; the user's server MUST also send that unavailable presence
  stanza to any of the user's other available resources, as well as to
  any entities to which the user has sent directed presence during the
  user's session for that resource (if the user has not yet sent
  directed unavailable presence to that entity).  Any presence stanza
  with no 'type' attribute and no 'to' attribute that is sent after
  sending directed unavailable presence or broadcasted unavailable
  presence MUST be broadcasted by the server to all subscribers.

5.1.6.  Presence Subscriptions

  A subscription request is a presence stanza whose 'type' attribute
  has a value of "subscribe".  If the subscription request is being
  sent to an instant messaging contact, the JID supplied in the 'to'
  attribute SHOULD be of the form <[email protected]> rather than
  <[email protected]/resource>, since the desired result is normally
  for the user to receive presence from all of the contact's resources,
  not merely the particular resource specified in the 'to' attribute.

  A user's server MUST NOT automatically approve subscription requests
  on the user's behalf.  All subscription requests MUST be directed to
  the user's client, specifically to one or more available resources
  associated with the user.  If there is no available resource
  associated with the user when the subscription request is received by
  the user's server, the user's server MUST keep a record of the
  subscription request and deliver the request when the user next
  creates an available resource, until the user either approves or
  denies the request.  If there is more than one available resource
  associated with the user when the subscription request is received by
  the user's server, the user's server MUST broadcast that subscription
  request to all available resources in accordance with Server Rules
  for Handling XML Stanzas (Section 11).  (Note: If an active resource



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  has not provided initial presence, the server MUST NOT consider it to
  be available and therefore MUST NOT send subscription requests to
  it.)   However, if the user receives a presence stanza of type
  "subscribe" from a contact to whom the user has already granted
  permission to see the user's presence information (e.g., in cases
  when the contact is seeking to resynchronize subscription states),
  the user's server SHOULD auto-reply on behalf of the user.  In
  addition, the user's server MAY choose to re-send an unapproved
  pending subscription request to the contact based on an
  implementation-specific algorithm (e.g., whenever a new resource
  becomes available for the user, or after a certain amount of time has
  elapsed); this helps to recover from transient, silent errors that
  may have occurred in relation to the original subscription request.

5.2.  Specifying Availability Status

  A client MAY provide further information about its availability
  status by using the <show/> element (see Show (Section 2.2.2.1)).

  Example: Availability status:

  <presence>
    <show>dnd</show>
  </presence>

5.3.  Specifying Detailed Status Information

  In conjunction with the <show/> element, a client MAY provide
  detailed status information by using the <status/> element (see
  Status (Section 2.2.2.2)).

  Example: Detailed status information:

  <presence xml:lang='en'>
    <show>dnd</show>
    <status>Wooing Juliet</status>
    <status xml:lang='cz'>Ja dvo&#x0159;&#x00ED;m Juliet</status>
  </presence>













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5.4.  Specifying Presence Priority

  A client MAY provide a priority for its resource by using the
  <priority/> element (see Priority (Section 2.2.2.3)).

  Example: Presence priority:

  <presence xml:lang='en'>
    <show>dnd</show>
    <status>Wooing Juliet</status>
    <status xml:lang='cz'>Ja dvo&#x0159;&#x00ED;m Juliet</status>
    <priority>1</priority>
  </presence>

5.5.  Presence Examples

  The examples in this section illustrate the presence-related
  protocols described above.  The user is [email protected], he has an
  available resource whose resource identifier is "orchard", and he has
  the following individuals in his roster:

  o  [email protected] (subscription="both" and she has two available
     resources, one whose resource is "chamber" and another whose
     resource is "balcony")

  o  [email protected] (subscription="to")

  o  [email protected] (subscription="from")

  Example 1: User sends initial presence:

  <presence/>

  Example 2: User's server sends presence probes to contacts with
  subscription="to" and subscription="both" on behalf of the user's
  available resource:

  <presence
      type='probe'
      from='[email protected]/orchard'
      to='[email protected]'/>

  <presence
      type='probe'
      from='[email protected]/orchard'
      to='[email protected]'/>





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  Example 3: User's server sends initial presence to contacts with
  subscription="from" and subscription="both" on behalf of the user's
  available resource:

  <presence
      from='[email protected]/orchard'
      to='[email protected]'/>

  <presence
      from='[email protected]/orchard'
      to='[email protected]'/>

  Example 4: Contacts' servers reply to presence probe on behalf of all
  available resources:

  <presence
      from='[email protected]/balcony'
      to='[email protected]/orchard'
      xml:lang='en'>
    <show>away</show>
    <status>be right back</status>
    <priority>0</priority>
  </presence>

  <presence
      from='[email protected]/chamber'
      to='[email protected]/orchard'>
    <priority>1</priority>
  </presence>

  <presence
      from='[email protected]/pda'
      to='[email protected]/orchard'
      xml:lang='en'>
    <show>dnd</show>
    <status>gallivanting</status>
  </presence>

  Example 5: Contacts' servers deliver user's initial presence to all
  available resources or return error to user:

  <presence
      from='[email protected]/orchard'
      to='[email protected]/chamber'/>







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  <presence
      from='[email protected]/orchard'
      to='[email protected]/balcony'/>

  <presence
      type='error'
      from='[email protected]'
      to='[email protected]/orchard'>
    <error type='cancel'>
      <gone xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    </error>
  </presence>

  Example 6: User sends directed presence to another user not in his
  roster:

  <presence
      from='[email protected]/orchard'
      to='[email protected]'
      xml:lang='en'>
    <show>dnd</show>
    <status>courting Juliet</status>
    <priority>0</priority>
  </presence>

  Example 7: User sends updated available presence information for
  broadcasting:

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

  Example 8: User's server broadcasts updated presence information only
  to one contact (not those from whom an error was received or to whom
  the user sent directed presence):

  <presence
      from='[email protected]/orchard'
      to='[email protected]'
      xml:lang='en'>
    <show>away</show>
    <status>I shall return!</status>
    <priority>1</priority>
  </presence>





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  Example 9: Contact's server delivers updated presence information to
  all of the contact's available resources:

  [to "balcony" resource...]
  <presence
      from='[email protected]/orchard'
      to='[email protected]'
      xml:lang='en'>
    <show>away</show>
    <status>I shall return!</status>
    <priority>1</priority>
  </presence>

  [to "chamber" resource...]
  <presence
      from='[email protected]/orchard'
      to='[email protected]'
      xml:lang='en'>
    <show>away</show>
    <status>I shall return!</status>
    <priority>1</priority>
  </presence>

  Example 10: One of the contact's resources broadcasts final presence:

  <presence from='[email protected]/balcony' type='unavailable'/>

  Example 11: Contact's server sends unavailable presence information
  to user:

  <presence
      type='unavailable'
      from='[email protected]/balcony'
      to='[email protected]/orchard'/>

  Example 12: User sends final presence:

  <presence from='[email protected]/orchard'
            type='unavailable'
            xml:lang='en'>
    <status>gone home</status>
  </presence>









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  Example 13: User's server broadcasts unavailable presence information
  to contact as well as to the person to whom the user sent directed
  presence:

  <presence
      type='unavailable'
      from='[email protected]/orchard'
      to='[email protected]'
      xml:lang='en'>
    <status>gone home</status>
  </presence>

  <presence
      from='[email protected]/orchard'
      to='[email protected]'
      xml:lang='en'>
    <status>gone home</status>
  </presence>

6.  Managing Subscriptions

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

  Note: There are important interactions between subscriptions and
  rosters; these are defined under Integration of Roster Items and
  Presence Subscriptions (Section 8), and the reader must refer to that
  section for a complete understanding of presence subscriptions.

6.1.  Requesting a Subscription

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

  Example: Sending a subscription request:

  <presence to='[email protected]' type='subscribe'/>






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  For client and server responsibilities regarding presence
  subscription requests, refer to Presence Subscriptions (Section
  5.1.6).

6.2.  Handling a Subscription Request

  When a client receives a subscription request from another entity, it
  MUST either approve the request by sending a presence stanza of type
  "subscribed" or refuse the request by sending a presence stanza of
  type "unsubscribed".

  Example: Approving a subscription request:

  <presence to='[email protected]' type='subscribed'/>

  Example: Refusing a presence subscription request:

  <presence to='[email protected]' type='unsubscribed'/>

6.3.  Cancelling a Subscription from Another Entity

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

  Example: Cancelling a previously granted subscription request:

  <presence to='[email protected]' type='unsubscribed'/>

6.4.  Unsubscribing from Another Entity's Presence

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

  Example: Unsubscribing from an entity's presence:

  <presence to='[email protected]' type='unsubscribe'/>

7.  Roster Management

  In XMPP, one's contact list is called a roster, which consists of any
  number of specific roster items, each roster item being identified by
  a unique JID (usually of the form <contact@domain>).  A user's roster
  is stored by the user's server on the user's behalf so that the user
  may access roster information from any resource.







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  Note: There are important interactions between rosters and
  subscriptions; these are defined under Integration of Roster Items
  and Presence Subscriptions (Section 8), and the reader must refer to
  that section for a complete understanding of roster management.

7.1.  Syntax and Semantics

  Rosters are managed using IQ stanzas, specifically by means of a
  <query/> child element qualified by the 'jabber:iq:roster' namespace.
  The <query/> element MAY contain one or more <item/> children, each
  describing a unique roster item or "contact".

  The "key" or unique identifier for each roster item is a JID,
  encapsulated in the 'jid' attribute of the <item/> element (which is
  REQUIRED).  The value of the 'jid' attribute SHOULD be of the form
  <user@domain> if the item is associated with another (human) instant
  messaging user.

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

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

  o  "to" -- the user has a subscription to the contact's presence
     information, but the contact does not have a subscription to the
     user's presence information

  o  "from" -- the contact has a subscription to the user's presence
     information, but the user does not have a subscription to the
     contact's presence information

  o  "both" -- both the user and the contact have subscriptions to each
     other's presence information

  Each <item/> element MAY contain a 'name' attribute, which sets the
  "nickname" to be associated with the JID, as determined by the user
  (not the contact).  The value of the 'name' attribute is opaque.

  Each <item/> element MAY contain one or more <group/> child elements,
  for use in collecting roster items into various categories.  The XML
  character data of the <group/> element is opaque.







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7.2.  Business Rules

  A server MUST ignore any 'to' address on a roster "set", and MUST
  treat any roster "set" as applying to the sender.  For added safety,
  a client SHOULD check the "from" address of a "roster push" (incoming
  IQ of type "set" containing a roster item) to ensure that it is from
  a trusted source; specifically, the stanza MUST either have no 'from'
  attribute (i.e., implicitly from the server) or have a 'from'
  attribute whose value matches the user's bare JID (of the form
  <user@domain>) or full JID (of the form <user@domain/resource>);
  otherwise, the client SHOULD ignore the "roster push".

7.3.  Retrieving One's Roster on Login

  Upon connecting to the server and becoming an active resource, a
  client SHOULD request the roster before sending initial presence
  (however, because receiving the roster may not be desirable for all
  resources, e.g., a connection with limited bandwidth, the client's
  request for the roster is OPTIONAL).  If an available resource does
  not request the roster during a session, the server MUST NOT send it
  presence subscriptions and associated roster updates.

  Example: Client requests current roster from server:

  <iq from='[email protected]/balcony' type='get' id='roster_1'>
    <query xmlns='jabber:iq:roster'/>
  </iq>

  Example: Client receives roster from server:

  <iq to='[email protected]/balcony' type='result' id='roster_1'>
    <query xmlns='jabber:iq:roster'>
      <item jid='[email protected]'
            name='Romeo'
            subscription='both'>
        <group>Friends</group>
      </item>
      <item jid='[email protected]'
            name='Mercutio'
            subscription='from'>
        <group>Friends</group>
      </item>
      <item jid='[email protected]'
            name='Benvolio'
            subscription='both'>
        <group>Friends</group>
      </item>
    </query>



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  </iq>

7.4.  Adding a Roster Item

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

  Example: Client adds a new item:

  <iq from='[email protected]/balcony' type='set' id='roster_2'>
    <query xmlns='jabber:iq:roster'>
      <item jid='[email protected]'
            name='Nurse'>
        <group>Servants</group>
      </item>
    </query>
  </iq>

  The server MUST update the roster information in persistent storage,
  and also push the change out to all of the user's available resources
  that have requested the roster.  This "roster push" consists of an IQ
  stanza of type "set" from the server to the client and enables all
  available resources to remain in sync with the server-based roster
  information.

  Example: Server (1) pushes the updated roster information to all
  available resources that have requested the roster and (2) replies
  with an IQ result to the sending resource:

  <iq to='[email protected]/balcony'
      type='set'
      id='a78b4q6ha463'>
    <query xmlns='jabber:iq:roster'>
      <item jid='[email protected]'
            name='Nurse'
            subscription='none'>
        <group>Servants</group>
      </item>
    </query>
  </iq>

  <iq to='[email protected]/chamber'
      type='set'
      id='a78b4q6ha464'>
    <query xmlns='jabber:iq:roster'>
      <item jid='[email protected]'
            name='Nurse'
            subscription='none'>
        <group>Servants</group>



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      </item>
    </query>
  </iq>

  <iq to='[email protected]/balcony' type='result' id='roster_2'/>

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

  Example: Resources reply with an IQ result to the server:

  <iq from='[email protected]/balcony'
      to='example.com'
      type='result'
      id='a78b4q6ha463'/>
  <iq from='[email protected]/chamber'
      to='example.com'
      type='result'
      id='a78b4q6ha464'/>

7.5.  Updating a Roster Item

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

  Example: User updates roster item (added group):

  <iq from='[email protected]/chamber' type='set' id='roster_3'>
    <query xmlns='jabber:iq:roster'>
      <item jid='[email protected]'
            name='Romeo'
            subscription='both'>
        <group>Friends</group>
        <group>Lovers</group>
      </item>
    </query>
  </iq>

  As with adding a roster item, when updating a roster item the server
  MUST update the roster information in persistent storage, and also
  initiate a roster push to all of the user's available resources that
  have requested the roster.







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7.6.  Deleting a Roster Item

  At any time, a user MAY delete an item from his or her roster by
  sending an IQ set to the server 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).

  Example: Client removes an item:

  <iq from='[email protected]/balcony' type='set' id='roster_4'>
    <query xmlns='jabber:iq:roster'>
      <item jid='[email protected]' subscription='remove'/>
    </query>
  </iq>

  As with adding a roster item, when deleting a roster item the server
  MUST update the roster information in persistent storage, initiate a
  roster push to all of the user's available resources that have
  requested the roster (with the 'subscription' attribute set to a
  value of "remove"), and send an IQ result to the initiating resource.

  For further information about the implications of this command, see
  Removing a Roster Item and Cancelling All Subscriptions (Section
  8.6).

8.  Integration of Roster Items and Presence Subscriptions

8.1.  Overview

  Some level of integration between roster items and presence
  subscriptions is normally expected by an instant messaging user
  regarding the user's subscriptions to and from other contacts.  This
  section describes the level of integration that MUST be supported
  within XMPP instant messaging applications.

  There are four primary subscription states:

  o  None -- the user does not have a subscription to the contact's
     presence information, and the contact does not have a subscription
     to the user's presence information










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  o  To -- the user has a subscription to the contact's presence
     information, but the contact does not have a subscription to the
     user's presence information

  o  From -- the contact has a subscription to the user's presence
     information, but the user does not have a subscription to the
     contact's presence information

  o  Both -- both the user and the contact have subscriptions to each
     other's presence information (i.e., the union of 'from' and 'to')

  Each of these states is reflected in the roster of both the user and
  the contact, thus resulting in durable subscription states.

  Narrative explanations of how these subscription states interact with
  roster items in order to complete certain defined use cases are
  provided in the following sub-sections.  Full details regarding
  server and client handling of all subscription states (including
  pending states between the primary states listed above) is provided
  in Subscription States (Section 9).

  The server MUST NOT send presence subscription requests or roster
  pushes to unavailable resources, nor to available resources that have
  not requested the roster.

  The 'from' and 'to' addresses are OPTIONAL in roster pushes; if
  included, their values SHOULD be the full JID of the resource for
  that session.  A client MUST acknowledge each roster push with an IQ
  stanza of type "result" (for the sake of brevity, these stanzas are
  not shown in the following examples but are required by the IQ
  semantics defined in [XMPP-CORE]).

8.2.  User Subscribes to Contact

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

  1.  In preparation for being able to render the contact in the user's
      client interface and for the server to keep track of the
      subscription, the user's client SHOULD perform a "roster set" for
      the new roster item.  This request consists of sending an IQ
      stanza of type='set' containing a <query/> element qualified by
      the 'jabber:iq:roster' namespace, which in turn contains an
      <item/> element that defines the new roster item; the <item/>
      element MUST possess a 'jid' attribute, MAY possess a 'name'
      attribute, MUST NOT possess a 'subscription' attribute, and MAY
      contain one or more <group/> child elements:



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  <iq type='set' id='set1'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          name='MyContact'>
        <group>MyBuddies</group>
      </item>
    </query>
  </iq>

  2.  As a result, the user's server (1) MUST initiate a roster push
      for the new roster item to all available resources associated
      with this user that have requested the roster, setting the
      'subscription' attribute to a value of "none"; and (2) MUST reply
      to the sending resource with an IQ result indicating the success
      of the roster set:

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='none'
          name='MyContact'>
        <group>MyBuddies</group>
      </item>
    </query>
  </iq>

  <iq type='result' id='set1'/>

  3.  If the user wants to request a subscription to the contact's
      presence information, the user's client MUST send a presence
      stanza of type='subscribe' to the contact:

  <presence to='[email protected]' type='subscribe'/>

  4.  As a result, the user's server MUST initiate a second roster push
      to all of the user's available resources that have requested the
      roster, setting the contact to the pending sub-state of the
      'none' subscription state; this pending sub-state is denoted by
      the inclusion of the ask='subscribe' attribute in the roster
      item:









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  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='none'
          ask='subscribe'
          name='MyContact'>
        <group>MyBuddies</group>
      </item>
    </query>
  </iq>

  Note: If the user did not create a roster item before sending the
  subscription request, the server MUST now create one on behalf of the
  user, then send a roster push to all of the user's available
  resources that have requested the roster, absent the 'name' attribute
  and the <group/> child shown above.

  5.  The user's server MUST also stamp the presence stanza of type
      "subscribe" with the user's bare JID (i.e., <[email protected]>)
      as the 'from' address (if the user provided a 'from' address set
      to the user's full JID, the server SHOULD remove the resource
      identifier).  If the contact is served by a different host than
      the user, the user's server MUST route the presence stanza to the
      contact's server for delivery to the contact (this case is
      assumed throughout; however, if the contact is served by the same
      host, then the server can simply deliver the presence stanza
      directly):

  <presence
      from='[email protected]'
      to='[email protected]'
      type='subscribe'/>

  Note: If the user's server receives a presence stanza of type "error"
  from the contact's server, it MUST deliver the error stanza to the
  user, whose client MAY determine that the error is in response to the
  outgoing presence stanza of type "subscribe" it sent previously
  (e.g., by tracking an 'id' attribute) and then choose to resend the
  "subscribe" request or revert the roster to its previous state by
  sending a presence stanza of type "unsubscribe" to the contact.

  6.  Upon receiving the presence stanza of type "subscribe" addressed
      to the contact, the contact's server MUST determine if there is
      at least one available resource from which the contact has
      requested the roster.  If so, it MUST deliver the subscription
      request to the contact (if not, the contact's server MUST store
      the subscription request offline for delivery when this condition



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      is next met; normally this is done by adding a roster item for
      the contact to the user's roster, with a state of "None + Pending
      In" as defined under Subscription States (Section 9), however a
      server SHOULD NOT push or deliver roster items in that state to
      the contact).  No matter when the subscription request is
      delivered, the contact must decide whether or not to approve it
      (subject to the contact's configured preferences, the contact's
      client MAY approve or refuse the subscription request without
      presenting it to the contact).  Here we assume the "happy path"
      that the contact approves the subscription request (the alternate
      flow of declining the subscription request is defined in Section
      8.2.1).  In this case, the contact's client (1) SHOULD perform a
      roster set specifying the desired nickname and group for the user
      (if any); and (2) MUST send a presence stanza of type
      "subscribed" to the user in order to approve the subscription
      request.

  <iq type='set' id='set2'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          name='SomeUser'>
        <group>SomeGroup</group>
      </item>
    </query>
  </iq>

  <presence to='[email protected]' type='subscribed'/>

  7.  As a result, the contact's server (1) MUST initiate a roster push
      to all available resources associated with the contact that have
      requested the roster, containing a roster item for the user with
      the subscription state set to 'from' (the server MUST send this
      even if the contact did not perform a roster set); (2) MUST
      return an IQ result to the sending resource indicating the
      success of the roster set; (3) MUST route the presence stanza of
      type "subscribed" to the user, first stamping the 'from' address
      as the bare JID (<[email protected]>) of the contact; and (4)
      MUST send available presence from all of the contact's available
      resources to the user:











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  <iq type='set' to='[email protected]/resource'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='from'
          name='SomeUser'>
        <group>SomeGroup</group>
      </item>
    </query>
  </iq>

  <iq type='result' to='[email protected]/resource' id='set2'/>

  <presence
      from='[email protected]'
      to='[email protected]'
      type='subscribed'/>

  <presence
      from='[email protected]/resource'
      to='[email protected]'/>

  Note: If the contact's server receives a presence stanza of type
  "error" from the user's server, it MUST deliver the error stanza to
  the contact, whose client MAY determine that the error is in response
  to the outgoing presence stanza of type "subscribed" it sent
  previously (e.g., by tracking an 'id' attribute) and then choose to
  resend the "subscribed" notification or revert the roster to its
  previous state by sending a presence stanza of type "unsubscribed" to
  the user.

  8.  Upon receiving the presence stanza of type "subscribed" addressed
      to the user, the user's server MUST first verify that the contact
      is in the user's roster with either of the following states: (a)
      subscription='none' and ask='subscribe' or (b)
      subscription='from' and ask='subscribe'.  If the contact is not
      in the user's roster with either of those states, the user's
      server MUST silently ignore the presence stanza of type
      "subscribed" (i.e., it MUST NOT route it to the user, modify the
      user's roster, or generate a roster push to the user's available
      resources).  If the contact is in the user's roster with either
      of those states, the user's server (1) MUST deliver the presence
      stanza of type "subscribed" from the contact to the user; (2)
      MUST initiate a roster push to all of the user's available
      resources that have requested the roster, containing an updated
      roster item for the contact with the 'subscription' attribute set





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      to a value of "to"; and (3) MUST deliver the available presence
      stanza received from each of the contact's available resources to
      each of the user's available resources:

  <presence
      to='[email protected]'
      from='[email protected]'
      type='subscribed'/>

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='to'
          name='MyContact'>
        <group>MyBuddies</group>
      </item>
    </query>
  </iq>

  <presence
      from='[email protected]/resource'
      to='[email protected]/resource'/>

  9.  Upon receiving the presence stanza of type "subscribed", the user
      SHOULD acknowledge receipt of that subscription state
      notification through either "affirming" it by sending a presence
      stanza of type "subscribe" to the contact or "denying" it by
      sending a presence stanza of type "unsubscribe" to the contact;
      this step does not necessarily affect the subscription state (see
      Subscription States (Section 9) for details), but instead lets
      the user's server know that it MUST no longer send notification
      of the subscription state change to the user (see Section 9.4).

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

8.2.1.  Alternate Flow: Contact Declines Subscription Request

  The above activity flow represents the "happy path" regarding the
  user's subscription request to the contact.  The main alternate flow
  occurs if the contact refuses the user's subscription request, as
  described below.







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  1.  If the contact wants to refuse the request, the contact's client
      MUST send a presence stanza of type "unsubscribed" to the user
      (instead of the presence stanza of type "subscribed" sent in Step
      6 of Section 8.2):

  <presence to='[email protected]' type='unsubscribed'/>

  2.  As a result, the contact's server MUST route the presence stanza
      of type "unsubscribed" to the user, first stamping the 'from'
      address as the bare JID (<[email protected]>) of the contact:

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>

  Note: If the contact's server previously added the user to the
  contact's roster for tracking purposes, it MUST remove the relevant
  item at this time.

  3.  Upon receiving the presence stanza of type "unsubscribed"
      addressed to the user, the user's server (1) MUST deliver that
      presence stanza to the user and (2) MUST initiate a roster push
      to all of the user's available resources that have requested the
      roster, containing an updated roster item for the contact with
      the 'subscription' attribute set to a value of "none" and with no
      'ask' attribute:

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='none'
          name='MyContact'>
        <group>MyBuddies</group>
      </item>
    </query>
  </iq>

  4.  Upon receiving the presence stanza of type "unsubscribed", the
      user SHOULD acknowledge receipt of that subscription state
      notification through either "affirming" it by sending a presence
      stanza of type "unsubscribe" to the contact or "denying" it by



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      sending a presence stanza of type "subscribe" to the contact;
      this step does not necessarily affect the subscription state (see
      Subscription States (Section 9) for details), but instead lets
      the user's server know that it MUST no longer send notification
      of the subscription state change to the user (see Section 9.4).

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

8.3.  Creating a Mutual Subscription

  The user and contact can build on the "happy path" described above to
  create a mutual subscription (i.e., a subscription of type "both").
  The process is described below.

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

  <presence to='[email protected]' type='subscribe'/>

  2.  As a result, the contact's server (1) MUST initiate a roster push
      to all available resources associated with the contact that have
      requested the roster, with the user still in the 'from'
      subscription state but with a pending 'to' subscription denoted
      by the inclusion of the ask='subscribe' attribute in the roster
      item; and (2) MUST route the presence stanza of type "subscribe"
      to the user, first stamping the 'from' address as the bare JID
      (<[email protected]>) of the contact:

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='from'
          ask='subscribe'
          name='SomeUser'>
        <group>SomeGroup</group>
      </item>
    </query>
  </iq>








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  <presence
      from='[email protected]'
      to='[email protected]'
      type='subscribe'/>

  Note: If the contact's server receives a presence stanza of type
  "error" from the user's server, it MUST deliver the error stanza to
  the contact, whose client MAY determine that the error is in response
  to the outgoing presence stanza of type "subscribe" it sent
  previously (e.g., by tracking an 'id' attribute) and then choose to
  resend the "subscribe" request or revert the roster to its previous
  state by sending a presence stanza of type "unsubscribe" to the user.

  3.  Upon receiving the presence stanza of type "subscribe" addressed
      to the user, the user's server must determine if there is at
      least one available resource for which the user has requested the
      roster.  If so, the user's server MUST deliver the subscription
      request to the user (if not, it MUST store the subscription
      request offline for delivery when this condition is next met). No
      matter when the subscription request is delivered, the user must
      then decide whether or not to approve it (subject to the user's
      configured preferences, the user's client MAY approve or refuse
      the subscription request without presenting it to the user).
      Here we assume the "happy path" that the user approves the
      subscription request (the alternate flow of declining the
      subscription request is defined in Section 8.3.1).  In this case,
      the user's client MUST send a presence stanza of type
      "subscribed" to the contact in order to approve the subscription
      request.

  <presence to='[email protected]' type='subscribed'/>

  4.  As a result, the user's server (1) MUST initiate a roster push to
      all of the user's available resources that have requested the
      roster, containing a roster item for the contact with the
      'subscription' attribute set to a value of "both"; (2) MUST route
      the presence stanza of type "subscribed" to the contact, first
      stamping the 'from' address as the bare JID (<[email protected]>)
      of the user; and (3) MUST send to the contact the full XML of the
      last presence stanza with no 'to' attribute received by the
      server from each of the user's available resources (subject to
      privacy lists in force for each session):









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  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='both'
          name='MyContact'>
        <group>MyBuddies</group>
      </item>
    </query>
  </iq>

  <presence
      from='[email protected]'
      to='[email protected]'
      type='subscribed'/>

  <presence
      from='[email protected]/resource'
      to='[email protected]'/>

  Note: If the user's server receives a presence stanza of type "error"
  from the contact's server, it MUST deliver the error stanza to the
  user, whose client MAY determine that the error is in response to the
  outgoing presence stanza of type "subscribed" it sent previously
  (e.g., by tracking an 'id' attribute) and then choose to resend the
  subscription request or revert the roster to its previous state by
  sending a presence stanza of type "unsubscribed" to the contact.

  5.  Upon receiving the presence stanza of type "subscribed" addressed
      to the contact, the contact's server MUST first verify that the
      user is in the contact's roster with either of the following
      states: (a) subscription='none' and ask='subscribe' or (b)
      subscription='from' and ask='subscribe'.  If the user is not in
      the contact's roster with either of those states, the contact's
      server MUST silently ignore the presence stanza of type
      "subscribed" (i.e., it MUST NOT route it to the contact, modify
      the contact's roster, or generate a roster push to the contact's
      available resources).  If the user is in the contact's roster
      with either of those states, the contact's server (1) MUST
      deliver the presence stanza of type "subscribed" from the user to
      the contact; (2) MUST initiate a roster push to all available
      resources associated with the contact that have requested the
      roster, containing an updated roster item for the user with the
      'subscription' attribute set to a value of "both"; and (3) MUST
      deliver the available presence stanza received from each of the
      user's available resources to each of the contact's available
      resources:




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  <presence
      from='[email protected]'
      to='[email protected]'
      type='subscribed'/>

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='both'
          name='SomeUser'>
        <group>SomeGroup</group>
      </item>
    </query>
  </iq>

  <presence
      from='[email protected]/resource'
      to='[email protected]/resource'/>

  6.  Upon receiving the presence stanza of type "subscribed", the
      contact SHOULD acknowledge receipt of that subscription state
      notification through either "affirming" it by sending a presence
      stanza of type "subscribe" to the user or "denying" it by sending
      a presence stanza of type "unsubscribe" to the user; this step
      does not necessarily affect the subscription state (see
      Subscription States (Section 9) for details), but instead lets
      the contact's server know that it MUST no longer send
      notification of the subscription state change to the contact (see
      Section 9.4).

  The user and the contact now have a mutual subscription to each
  other's presence -- i.e., the subscription is of type "both".

8.3.1.  Alternate Flow: User Declines Subscription Request

  The above activity flow represents the "happy path" regarding the
  contact's subscription request to the user.  The main alternate flow
  occurs if the user refuses the contact's subscription request, as
  described below.

  1.  If the user wants to refuse the request, the user's client MUST
      send a presence stanza of type "unsubscribed" to the contact
      (instead of the presence stanza of type "subscribed" sent in Step
      3 of Section 8.3):

  <presence to='[email protected]' type='unsubscribed'/>




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  2.  As a result, the user's server MUST route the presence stanza of
      type "unsubscribed" to the contact, first stamping the 'from'
      address as the bare JID (<[email protected]>) of the user:

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>

  3.  Upon receiving the presence stanza of type "unsubscribed"
      addressed to the contact, the contact's server (1) MUST deliver
      that presence stanza to the contact; and (2) MUST initiate a
      roster push to all available resources associated with the
      contact that have requested the roster, containing an updated
      roster item for the user with the 'subscription' attribute set to
      a value of "from" and with no 'ask' attribute:

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='from'
          name='SomeUser'>
        <group>SomeGroup</group>
      </item>
    </query>
  </iq>

  4.  Upon receiving the presence stanza of type "unsubscribed", the
      contact SHOULD acknowledge receipt of that subscription state
      notification through either "affirming" it by sending a presence
      stanza of type "unsubscribe" to the user or "denying" it by
      sending a presence stanza of type "subscribe" to the user; this
      step does not necessarily affect the subscription state (see
      Subscription States (Section 9) for details), but instead lets
      the contact's server know that it MUST no longer send
      notification of the subscription state change to the contact (see
      Section 9.4).

  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".



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8.4.  Unsubscribing

  At any time after subscribing to a contact's presence information, 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
  described below.

8.4.1.  Case #1: Unsubscribing When Subscription is Not Mutual

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

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

  <presence to='[email protected]' type='unsubscribe'/>

  2.  As a result, the user's server (1) MUST send a roster push to all
      of the user's available resources that have requested the roster,
      containing an updated roster item for the contact with the
      'subscription' attribute set to a value of "none"; and (2) MUST
      route the presence stanza of type "unsubscribe" to the contact,
      first stamping the 'from' address as the bare JID
      (<[email protected]>) of the user:

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='none'
          name='MyContact'>
        <group>MyBuddies</group>
      </item>
    </query>
  </iq>

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribe'/>






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  3.  Upon receiving the presence stanza of type "unsubscribe"
      addressed to the contact, the contact's server (1) MUST initiate
      a roster push to all available resources associated with the
      contact that have requested the roster, containing an updated
      roster item for the user with the 'subscription' attribute set to
      a value of "none" (if the contact is unavailable or has not
      requested the roster, the contact's server MUST modify the roster
      item and send that modified item the next time the contact
      requests the roster); and (2) MUST deliver the "unsubscribe"
      state change notification to the contact:

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='none'
          name='SomeUser'>
        <group>SomeGroup</group>
      </item>
    </query>
  </iq>

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribe'/>

  4.  Upon receiving the presence stanza of type "unsubscribe", the
      contact SHOULD acknowledge receipt of that subscription state
      notification through either "affirming" it by sending a presence
      stanza of type "unsubscribed" to the user or "denying" it by
      sending a presence stanza of type "subscribed" to the user; this
      step does not necessarily affect the subscription state (see
      Subscription States (Section 9) for details), but instead lets
      the contact's server know that it MUST no longer send
      notification of the subscription state change to the contact (see
      Section 9.4).

  5.  The contact's server then (1) MUST send a presence stanza of type
      "unsubscribed" to the user; and (2) SHOULD send unavailable
      presence from all of the contact's available resources to the
      user:

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>




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  <presence
      from='[email protected]/resource'
      to='[email protected]'
      type='unavailable'/>

  6.  When the user's server receives the presence stanzas of type
      "unsubscribed" and "unavailable", it MUST deliver them to the
      user:

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>

  <presence
      from='[email protected]/resource'
      to='[email protected]'
      type='unavailable'/>

  7.  Upon receiving the presence stanza of type "unsubscribed", the
      user SHOULD acknowledge receipt of that subscription state
      notification through either "affirming" it by sending a presence
      stanza of type "unsubscribe" to the contact or "denying" it by
      sending a presence stanza of type "subscribe" to the contact;
      this step does not necessarily affect the subscription state (see
      Subscription States (Section 9) for details), but instead lets
      the user's server know that it MUST no longer send notification
      of the subscription state change to the user (see Section 9.4).

8.4.2.  Case #2: Unsubscribing When Subscription is Mutual

  In the second case, the user has a subscription to the contact's
  presence information and the contact also has a subscription to the
  user's presence information (i.e., the subscription is mutual).

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

  <presence to='[email protected]' type='unsubscribe'/>

  2.  As a result, the user's server (1) MUST send a roster push to all
      of the user's available resources that have requested the roster,
      containing an updated roster item for the contact with the
      'subscription' attribute set to a value of "from"; and (2) MUST
      route the presence stanza of type "unsubscribe" to the contact,
      first stamping the 'from' address as the bare JID
      (<[email protected]>) of the user:



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  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='from'
          name='MyContact'>
        <group>MyBuddies</group>
      </item>
    </query>
  </iq>

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribe'/>

  3.  Upon receiving the presence stanza of type "unsubscribe"
      addressed to the contact, the contact's server (1) MUST initiate
      a roster push to all available resources associated with the
      contact that have requested the roster, containing an updated
      roster item for the user with the 'subscription' attribute set to
      a value of "to" (if the contact is unavailable or has not
      requested the roster, the contact's server MUST modify the roster
      item and send that modified item the next time the contact
      requests the roster); and (2) MUST deliver the "unsubscribe"
      state change notification to the contact:

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='to'
          name='SomeUser'>
        <group>SomeGroup</group>
      </item>
    </query>
  </iq>

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribe'/>

  4.  Upon receiving the presence stanza of type "unsubscribe", the
      contact SHOULD acknowledge receipt of that subscription state
      notification through either "affirming" it by sending a presence
      stanza of type "unsubscribed" to the user or "denying" it by
      sending a presence stanza of type "subscribed" to the user; this



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      step does not necessarily affect the subscription state (see
      Subscription States (Section 9) for details), but instead lets
      the contact's server know that it MUST no longer send
      notification of the subscription state change to the contact (see
      Section 9.4).

  5.  The contact's server then (1) MUST send a presence stanza of type
      "unsubscribed" to the user; and (2) SHOULD send unavailable
      presence from all of the contact's available resources to the
      user:

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>

  <presence
      from='[email protected]/resource'
      to='[email protected]'
      type='unavailable'/>

  6.  When the user's server receives the presence stanzas of type
      "unsubscribed" and "unavailable", it MUST deliver them to the
      user:

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>

  <presence
      from='[email protected]/resource'
      to='[email protected]'
      type='unavailable'/>

  7.  Upon receiving the presence stanza of type "unsubscribed", the
      user SHOULD acknowledge receipt of that subscription state
      notification through either "affirming" it by sending a presence
      stanza of type "unsubscribe" to the contact or "denying" it by
      sending a presence stanza of type "subscribe" to the contact;
      this step does not necessarily affect the subscription state (see
      Subscription States (Section 9) for details), but instead lets
      the user's server know that it MUST no longer send notification
      of the subscription state change to the user (see Section 9.4).

  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 information.  In order to both completely cancel



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  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 under Removing a Roster Item and
  Cancelling All Subscriptions (Section 8.6).

8.5.  Cancelling a Subscription

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

8.5.1.  Case #1: Cancelling When Subscription is Not Mutual

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

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

  <presence to='[email protected]' type='unsubscribed'/>

  2.  As a result, the contact's server (1) MUST send a roster push to
      all of the contact's available resources that have requested the
      roster, containing an updated roster item for the user with the
      'subscription' attribute set to a value of "none"; (2) MUST route
      the presence stanza of type "unsubscribed" to the user, first
      stamping the 'from' address as the bare JID
      (<[email protected]>) of the contact; and (3) SHOULD send
      unavailable presence from all of the contact's available
      resources to the user:

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='none'
          name='SomeUser'>
        <group>SomeGroup</group>
      </item>
    </query>
  </iq>




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  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>

  <presence
      from='[email protected]/resource'
      to='[email protected]'
      type='unavailable'/>

  3.  Upon receiving the presence stanza of type "unsubscribed"
      addressed to the user, the user's server (1) MUST initiate a
      roster push to all of the user's available resources that have
      requested the roster, containing an updated roster item for the
      contact with the 'subscription' attribute set to a value of
      "none" (if the user is unavailable or has not requested the
      roster, the user's server MUST modify the roster item and send
      that modified item the next time the user requests the roster);
      (2) MUST deliver the "unsubscribed" state change notification to
      all of the user's available resources; and (3) MUST deliver the
      unavailable presence to all of the user's available resources:

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='none'
          name='MyContact'>
        <group>MyBuddies</group>
      </item>
    </query>
  </iq>

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>

  <presence
      from='[email protected]/resource'
      to='[email protected]'
      type='unavailable'/>

  4.  Upon receiving the presence stanza of type "unsubscribed", the
      user SHOULD acknowledge receipt of that subscription state
      notification through either "affirming" it by sending a presence
      stanza of type "unsubscribe" to the contact or "denying" it by
      sending a presence stanza of type "subscribe" to the contact;



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      this step does not necessarily affect the subscription state (see
      Subscription States (Section 9) for details), but instead lets
      the user's server know that it MUST no longer send notification
      of the subscription state change to the user (see Section 9.4).

8.5.2.  Case #2: Cancelling When Subscription is Mutual

  In the second case, the user has a subscription to the contact's
  presence information and the contact also has a subscription to the
  user's presence information (i.e., the subscription is mutual).

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

  <presence to='[email protected]' type='unsubscribed'/>

  2.  As a result, the contact's server (1) MUST send a roster push to
      all of the contact's available resources that have requested the
      roster, containing an updated roster item for the user with the
      'subscription' attribute set to a value of "to"; (2) MUST route
      the presence stanza of type "unsubscribed" to the user, first
      stamping the 'from' address as the bare JID
      (<[email protected]>) of the contact; and (3) SHOULD send
      unavailable presence from all of the contact's available
      resources to all of the user's available resources:

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='to'
          name='SomeUser'>
        <group>SomeGroup</group>
      </item>
    </query>
  </iq>

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>

  <presence
      from='[email protected]/resource'
      to='[email protected]'
      type='unavailable'/>




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  3.  Upon receiving the presence stanza of type "unsubscribed"
      addressed to the user, the user's server (1) MUST initiate a
      roster push to all of the user's available resources that have
      requested the roster, containing an updated roster item for the
      contact with the 'subscription' attribute set to a value of
      "from" (if the user is unavailable or has not requested the
      roster, the user's server MUST modify the roster item and send
      that modified item the next time the user requests the roster);
      and (2) MUST deliver the "unsubscribed" state change notification
      to all of the user's available resources; and (3) MUST deliver
      the unavailable presence to all of the user's available
      resources:

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='from'
          name='MyContact'>
        <group>MyBuddies</group>
      </item>
    </query>
  </iq>

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>

  <presence
      from='[email protected]/resource'
      to='[email protected]'
      type='unavailable'/>

  4.  Upon receiving the presence stanza of type "unsubscribed", the
      user SHOULD acknowledge receipt of that subscription state
      notification through either "affirming" it by sending a presence
      stanza of type "unsubscribe" to the contact or "denying" it by
      sending a presence stanza of type "subscribe" to the contact;
      this step does not necessarily affect the subscription state (see
      Subscription States (Section 9) for details), but instead lets
      the user's server know that it MUST no longer send notification
      of the subscription state change to the user (see Section 9.4).

  Note: Obviously this does not result in removal of the roster item
  from the contact's roster, and the contact still has a subscription
  to the user's presence information.  In order to both completely
  cancel a mutual subscription and fully remove the roster item from



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  the contact's roster, the contact should update the roster item with
  subscription='remove' as defined under Removing a Roster Item and
  Cancelling All Subscriptions (Section 8.6).

8.6.  Removing a Roster Item and Cancelling All Subscriptions

  Because there may be many steps involved in completely removing a
  roster item and cancelling subscriptions in both directions, the
  roster management protocol includes a "shortcut" method for doing so.
  The process may be initiated no matter what the current subscription
  state is by sending a roster set containing an item for the contact
  with the 'subscription' attribute set to a value of "remove":

  <iq type='set' id='remove1'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='remove'/>
    </query>
  </iq>

  When the user removes a contact from his or her roster by setting the
  'subscription' attribute to a value of "remove", the user's server
  (1) MUST automatically cancel any existing presence subscription
  between the user and the contact (both 'to' and 'from' as
  appropriate); (2) MUST remove the roster item from the user's roster
  and inform all of the user's available resources that have requested
  the roster of the roster item removal; (3) MUST inform the resource
  that initiated the removal of success; and (4) SHOULD send
  unavailable presence from all of the user's available resources to
  the contact:

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribe'/>

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>










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  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='remove'/>
    </query>
  </iq>

  <iq type='result' id='remove1'/>

  <presence
      from='[email protected]/resource'
      to='[email protected]'
      type='unavailable'/>

  Upon receiving the presence stanza of type "unsubscribe", the
  contact's server (1) MUST initiate a roster push to all available
  resources associated with the contact that have requested the roster,
  containing an updated roster item for the user with the
  'subscription' attribute set to a value of "to" (if the contact is
  unavailable or has not requested the roster, the contact's server
  MUST modify the roster item and send that modified item the next time
  the contact requests the roster); and (2) MUST also deliver the
  "unsubscribe" state change notification to all of the contact's
  available resources:

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='to'
          name='SomeUser'>
        <group>SomeGroup</group>
      </item>
    </query>
  </iq>

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribe'/>

  Upon receiving the presence stanza of type "unsubscribed", the
  contact's server (1) MUST initiate a roster push to all available
  resources associated with the contact that have requested the roster,
  containing an updated roster item for the user with the
  'subscription' attribute set to a value of "none" (if the contact is
  unavailable or has not requested the roster, the contact's server



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  MUST modify the roster item and send that modified item the next time
  the contact requests the roster); and (2) MUST also deliver the
  "unsubscribe" state change notification to all of the contact's
  available resources:

  <iq type='set'>
    <query xmlns='jabber:iq:roster'>
      <item
          jid='[email protected]'
          subscription='none'
          name='SomeUser'>
        <group>SomeGroup</group>
      </item>
    </query>
  </iq>

  <presence
      from='[email protected]'
      to='[email protected]'
      type='unsubscribed'/>

  Upon receiving the presence stanza of type "unavailable" addressed to
  the contact, the contact's server MUST deliver the unavailable
  presence to all of the user's available resources:

  <presence
      from='[email protected]/resource'
      to='[email protected]'
      type='unavailable'/>

  Note: When the user removes the contact from the user's roster, the
  end state of the contact's roster is that the user is still in the
  contact's roster with a subscription state of "none"; in order to
  completely remove the roster item for the user, the contact needs to
  also send a roster removal request.

9.  Subscription States

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

9.1.  Defined States

  There are nine possible subscription states, which are described here
  from the user's (not contact's) perspective:




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  1.  "None" = contact and user are not subscribed to each other, and
      neither has requested a subscription from the other

  2.  "None + Pending Out" = contact and user are not subscribed to
      each other, and user has sent contact a subscription request but
      contact has not replied yet

  3.  "None + Pending In" = contact and user are not subscribed to each
      other, and contact has sent user a subscription request but user
      has not replied yet (note: contact's server SHOULD NOT push or
      deliver roster items in this state, but instead SHOULD wait until
      contact has approved subscription request from user)

  4.  "None + Pending Out/In" = contact and user are not subscribed to
      each other, contact has sent user a subscription request but user
      has not replied yet, and user has sent contact a subscription
      request but contact has not replied yet

  5.  "To" = user is subscribed to contact (one-way)

  6.  "To + Pending In" = user is subscribed to contact, and contact
      has sent user a subscription request but user has not replied yet

  7.  "From" = contact is subscribed to user (one-way)

  8.  "From + Pending Out" = contact is subscribed to user, and user
      has sent contact a subscription request but contact has not
      replied yet

  9.  "Both" = user and contact are subscribed to each other (two-way)

9.2.  Server Handling of Outbound Presence Subscription Stanzas

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

  Because it is possible for the user's server and the contact's server
  to lose synchronization regarding subscription states, the user's
  server MUST without exception route all outbound presence stanzas of
  type "subscribe" or "unsubscribe" to the contact so that the user is
  able to resynchronize his or her subscription to the contact's
  presence information if needed.






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  The user's server SHOULD NOT route a presence stanza of type
  "subscribed" or "unsubscribed" to the contact if the stanza does not
  result in a subscription state change from the user's perspective,
  and MUST NOT make a state change.  If the stanza results in a
  subscription state change, the user's server MUST route the stanza to
  the contact and MUST make the appropriate state change.  These rules
  are summarized in the following tables.

  Table 1: Recommended handling of outbound "subscribed" stanzas

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

  Table 2: Recommended handling of outbound "unsubscribed" stanzas

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

9.3.  Server Handling of Inbound Presence Subscription Stanzas

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



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  When the user's server receives a subscription request for the user
  from the contact (i.e., a presence stanza of type "subscribe"), it
  MUST deliver that request to the user for approval if the user has
  not already granted the contact access to the user's presence
  information and if there is no pending inbound subscription request;
  however, the user's server SHOULD NOT deliver the new request if
  there is a pending inbound subscription request, since the previous
  subscription request will have been recorded.  If the user has
  already granted the contact access to the user's presence
  information, the user's server SHOULD auto-reply to an inbound
  presence stanza of type "subscribe" from the contact by sending a
  presence stanza of type "subscribed" to the contact on behalf of the
  user; this rule enables the contact to resynchronize the subscription
  state if needed.  These rules are summarized in the following table.

  Table 3: Recommended handling of inbound "subscribe" stanzas

  +------------------------------------------------------------------+
  |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
  +------------------------------------------------------------------+
  |  "None"                  |  yes       |  "None + Pending In"     |
  |  "None + Pending Out"    |  yes       |  "None + Pending Out/In" |
  |  "None + Pending In"     |  no        |  no state change         |
  |  "None + Pending Out/In" |  no        |  no state change         |
  |  "To"                    |  yes       |  "To + Pending In"       |
  |  "To + Pending In"       |  no        |  no state change         |
  |  "From"                  |  no *      |  no state change         |
  |  "From + Pending Out"    |  no *      |  no state change         |
  |  "Both"                  |  no *      |  no state change         |
  +------------------------------------------------------------------+

  * Server SHOULD auto-reply with "subscribed" stanza

  When the user's server receives a presence stanza of type
  "unsubscribe" for the user from the contact, if the stanza results in
  a subscription state change from the user's perspective then the
  user's server SHOULD auto-reply by sending a presence stanza of type
  "unsubscribed" to the contact on behalf of the user, MUST deliver the
  "unsubscribe" stanza to the user, and MUST change the state.  If no
  subscription state change results, the user's server SHOULD NOT
  deliver the stanza and MUST NOT change the state.  These rules are
  summarized in the following table.









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  Table 4: Recommended handling of inbound "unsubscribe" stanzas

  +------------------------------------------------------------------+
  |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
  +------------------------------------------------------------------+
  |  "None"                  |  no        |  no state change         |
  |  "None + Pending Out"    |  no        |  no state change         |
  |  "None + Pending In"     |  yes *     |  "None"                  |
  |  "None + Pending Out/In" |  yes *     |  "None + Pending Out"    |
  |  "To"                    |  no        |  no state change         |
  |  "To + Pending In"       |  yes *     |  "To"                    |
  |  "From"                  |  yes *     |  "None"                  |
  |  "From + Pending Out"    |  yes *     |  "None + Pending Out     |
  |  "Both"                  |  yes *     |  "To"                    |
  +------------------------------------------------------------------+

  * Server SHOULD auto-reply with "unsubscribed" stanza

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

  Table 5: Recommended handling of inbound "subscribed" stanzas

  +------------------------------------------------------------------+
  |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
  +------------------------------------------------------------------+
  |  "None"                  |  no        |  no state change         |
  |  "None + Pending Out"    |  yes       |  "To"                    |
  |  "None + Pending In"     |  no        |  no state change         |
  |  "None + Pending Out/In" |  yes       |  "To + Pending In"       |
  |  "To"                    |  no        |  no state change         |
  |  "To + Pending In"       |  no        |  no state change         |
  |  "From"                  |  no        |  no state change         |
  |  "From + Pending Out"    |  yes       |  "Both"                  |
  |  "Both"                  |  no        |  no state change         |
  +------------------------------------------------------------------+



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

  Table 6: Recommended handling of inbound "unsubscribed" stanzas

  +------------------------------------------------------------------+
  |  EXISTING STATE          |  DELIVER?  |  NEW STATE               |
  +------------------------------------------------------------------+
  |  "None"                  |  no        |  no state change         |
  |  "None + Pending Out"    |  yes       |  "None"                  |
  |  "None + Pending In"     |  no        |  no state change         |
  |  "None + Pending Out/In" |  yes       |  "None + Pending In"     |
  |  "To"                    |  yes       |  "None"                  |
  |  "To + Pending In"       |  yes       |  "None + Pending In"     |
  |  "From"                  |  no        |  no state change         |
  |  "From + Pending Out"    |  yes       |  "From"                  |
  |  "Both"                  |  yes       |  "From"                  |
  +------------------------------------------------------------------+

9.4.  Server Delivery and Client Acknowledgement of Subscription
     Requests and State Change Notifications

  When a server receives an inbound presence stanza of type "subscribe"
  (i.e., a subscription request) or of type "subscribed",
  "unsubscribe", or "unsubscribed" (i.e., a subscription state change
  notification), in addition to sending the appropriate roster push (or
  updated roster when the roster is next requested by an available
  resource), it MUST deliver the request or notification to the
  intended recipient at least once.  A server MAY require the recipient
  to acknowledge receipt of all state change notifications (and MUST
  require acknowledgement in the case of subscription requests, i.e.,
  presence stanzas of type "subscribe").  In order to require
  acknowledgement, a server SHOULD send the request or notification to
  the recipient each time the recipient logs in, until the recipient
  acknowledges receipt of the notification by "affirming" or "denying"
  the notification, as shown in the following table:









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  Table 7: Acknowledgement of subscription state change notifications

  +--------------------------------------------------+
  |  STANZA TYPE   |  ACCEPT        |  DENY          |
  +--------------------------------------------------+
  |  subscribe     |  subscribed    |  unsubscribed  |
  |  subscribed    |  subscribe     |  unsubscribe   |
  |  unsubscribe   |  unsubscribed  |  subscribed    |
  |  unsubscribed  |  unsubscribe   |  subscribe     |
  +--------------------------------------------------+

  Obviously, given the foregoing subscription state charts, some of the
  acknowledgement stanzas will be routed to the contact and result in
  subscription state changes, while others will not.  However, any such
  stanzas MUST result in the server's no longer sending the
  subscription state notification to the user.

  Because a user's server MUST automatically generate outbound presence
  stanzas of type "unsubscribe" and "unsubscribed" upon receiving a
  roster set with the 'subscription' attribute set to a value of
  "remove" (see Removing a Roster Item and Cancelling All Subscriptions
  (Section 8.6)), the server MUST treat a roster remove request as
  equivalent to sending both of those presence stanzas for purposes of
  determining whether to continue sending subscription state change
  notifications of type "subscribe" or "subscribed" to the user.

10.  Blocking Communication

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

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

  o  Retrieving one's privacy lists.

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

  o  Setting, changing, or declining active lists.

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

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



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

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

  o  Allowing or blocking IQ stanzas based on JID, group, or
     subscription type (or globally).

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

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

10.1.  Syntax and Semantics

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

  The syntax is as follows:

  <iq>
    <query xmlns='jabber:iq:privacy'>
      <list name='foo'>
        <item
            type='[jid|group|subscription]'
            value='bar'
            action='[allow|deny]'
            order='unsignedInt'>
          [<message/>]
          [<presence-in/>]
          [<presence-out/>]
          [<iq/>]
        </item>
      </list>
    </query>
  </iq>






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  If the type is "jid", then the 'value' attribute MUST contain a valid
  Jabber ID.  JIDs SHOULD be matched in the following order:

  1.  <user@domain/resource> (only that resource matches)

  2.  <user@domain> (any resource matches)

  3.  <domain/resource> (only that resource matches)

  4.  <domain> (the domain itself matches, as does any user@domain,
      domain/resource, or address containing a subdomain)

  If the type is "group", then the 'value' attribute SHOULD contain the
  name of a group in the user's roster.  (If a client attempts to
  update, create, or delete a list item with a group that is not in the
  user's roster, the server SHOULD return to the client an
  <item-not-found/> stanza error.)

  If the type is "subscription", then the 'value' attribute MUST be one
  of "both", "to", "from", or "none" as defined under Roster Syntax and
  Semantics (Section 7.1), where "none" includes entities that are
  totally unknown to the user and therefore not in the user's roster at
  all.

  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
  "allow" or "deny".

  The 'order' attribute MUST be included and its value MUST be a
  non-negative integer that is unique among all items in the list.  (If
  a client attempts to create or update a list with non-unique order
  values, the server MUST return to the client a <bad-request/> stanza
  error.)

  The <item/> element MAY contain one or more child elements that
  enable an entity to specify more granular control over which kinds of
  stanzas are to be blocked (i.e., rather than blocking all stanzas).
  The allowable child elements are:

  o  <message/> -- blocks incoming message stanzas
  o  <iq/> -- blocks incoming IQ stanzas
  o  <presence-in/> -- blocks incoming presence notifications
  o  <presence-out/> -- blocks outgoing presence notifications






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  Within the 'jabber:iq:privacy' namespace, the <query/> child of an 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 sending entity
  violates this rule, the receiving entity MUST return a <bad-request/>
  stanza error.

  When a client adds or updates a privacy list, the <list/> element
  SHOULD contain at least one <item/> child element; when a client
  removes a privacy list, the <list/> element MUST NOT contain any
  <item/> child elements.

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

10.2.  Business Rules

  1.  If there is an active list set for a session, it affects only the
      session(s) for which it is activated, and only for the duration
      of the session(s); the server MUST apply the active list only and
      MUST NOT apply the default list (i.e., there is no "layering" of
      lists).

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

  3.  If there is no active list set for a session (or there are no
      current sessions for the user), and there is no default list,
      then all stanzas SHOULD BE accepted or appropriately processed by
      the server on behalf of the user in accordance with the Server
      Rules for Handling XML Stanzas (Section 11).

  4.  Privacy lists MUST be the first delivery rule applied by a
      server, superseding (1) the routing and delivery rules specified
      in Server Rules for Handling XML Stanzas (Section 11), and (2)
      the handling of subscription-related presence stanzas (and
      corresponding generation of roster pushes) specified in
      Integration of Roster Items and Presence Subscriptions (Section
      8).

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





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  6.  As soon as a stanza is matched against a privacy list rule, the
      server MUST appropriately handle the stanza in accordance with
      the rule and cease processing.

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

  8.  If a user updates the definition for an active list, subsequent
      processing based on that active list MUST use the updated
      definition (for all resources to which that active list currently
      applies).

  9.  If a change to the subscription state or roster group of a roster
      item defined in an active or default list occurs during a user's
      session, subsequent processing based on that list MUST take into
      account the changed state or group (for all resources to which
      that list currently applies).

  10. When the definition for a rule is modified, the server MUST send
      an IQ stanza of type "set" to all connected resources, containing
      a <query/> element with only one <list/> child element, where the
      'name' attribute is set to the name of the modified privacy list.
      These "privacy list pushes" adhere to the same semantics as the
      "roster pushes" used in roster management, except that only the
      list name itself (not the full list definition or the "delta") is
      pushed to the connected resources.  It is up to the receiving
      resource to determine whether to retrieve the modified list
      definition, although a connected resource SHOULD do so if the
      list currently applies to it.

  11. When a resource attempts to remove a list or specify a new
      default list while that list applies to a connected resource
      other than the sending resource, the server MUST return a
      <conflict/> error to the sending resource and MUST NOT make the
      requested change.

10.3.  Retrieving One's Privacy Lists

  Example: Client requests names of privacy lists from server:

  <iq from='[email protected]/orchard' type='get' id='getlist1'>
    <query xmlns='jabber:iq:privacy'/>
  </iq>








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  Example: Server sends names of privacy lists to client, preceded by
  active list and default list:

  <iq type='result' id='getlist1' to='[email protected]/orchard'>
    <query xmlns='jabber:iq:privacy'>
      <active name='private'/>
      <default name='public'/>
      <list name='public'/>
      <list name='private'/>
      <list name='special'/>
    </query>
  </iq>

  Example: Client requests a privacy list from server:

  <iq from='[email protected]/orchard' type='get' id='getlist2'>
    <query xmlns='jabber:iq:privacy'>
      <list name='public'/>
    </query>
  </iq>

  Example: Server sends a privacy list to client:

  <iq type='result' id='getlist2' to='[email protected]/orchard'>
    <query xmlns='jabber:iq:privacy'>
      <list name='public'>
        <item type='jid'
              value='[email protected]'
              action='deny'
              order='1'/>
        <item action='allow' order='2'/>
      </list>
    </query>
  </iq>

  Example: Client requests another privacy list from server:

  <iq from='[email protected]/orchard' type='get' id='getlist3'>
    <query xmlns='jabber:iq:privacy'>
      <list name='private'/>
    </query>
  </iq>









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  Example: Server sends another privacy list to client:

  <iq type='result' id='getlist3' to='[email protected]/orchard'>
    <query xmlns='jabber:iq:privacy'>
      <list name='private'>
        <item type='subscription'
              value='both'
              action='allow'
              order='10'/>
        <item action='deny' order='15'/>
      </list>
    </query>
  </iq>

  Example: Client requests yet another privacy list from server:

  <iq from='[email protected]/orchard' type='get' id='getlist4'>
    <query xmlns='jabber:iq:privacy'>
      <list name='special'/>
    </query>
  </iq>

  Example: Server sends yet another privacy list to client:

  <iq type='result' id='getlist4' to='[email protected]/orchard'>
    <query xmlns='jabber:iq:privacy'>
      <list name='special'>
        <item type='jid'
              value='[email protected]'
              action='allow'
              order='6'/>
        <item type='jid'
              value='[email protected]'
              action='allow'
              order='7'/>
        <item type='jid'
              value='[email protected]'
              action='allow'
              order='42'/>
        <item action='deny' order='666'/>
      </list>
    </query>
  </iq>

  In this example, the user has three lists: (1) 'public', which allows
  communications from everyone except one specific entity (this is the
  default list); (2) 'private', which allows communications only with




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  contacts who have a bidirectional subscription with the user (this is
  the active list); and (3) 'special', which allows communications only
  with three specific entities.

  If the user attempts to retrieve a list but a list by that name does
  not exist, the server MUST return an <item-not-found/> stanza error
  to the user:

  Example: Client attempts to retrieve non-existent list:

  <iq to='[email protected]/orchard' type='error' id='getlist5'>
    <query xmlns='jabber:iq:privacy'>
      <list name='The Empty Set'/>
    </query>
    <error type='cancel'>
      <item-not-found
          xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    </error>
  </iq>

  The user is allowed to retrieve only one list at a time.  If the user
  attempts to retrieve more than one list in the same request, the
  server MUST return a <bad request/> stanza error to the user:

  Example: Client attempts to retrieve more than one list:

  <iq to='[email protected]/orchard' type='error' id='getlist6'>
    <query xmlns='jabber:iq:privacy'>
      <list name='public'/>
      <list name='private'/>
      <list name='special'/>
    </query>
    <error type='modify'>
      <bad-request
          xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    </error>
  </iq>

10.4.  Managing Active Lists

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






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  Example: Client requests change of active list:

  <iq from='[email protected]/orchard' type='set' id='active1'>
    <query xmlns='jabber:iq:privacy'>
      <active name='special'/>
    </query>
  </iq>

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

  Example: Server acknowledges success of active list change:

  <iq type='result' id='active1' to='[email protected]/orchard'/>

  If the user attempts to set an active list but a list by that name
  does not exist, the server MUST return an <item-not-found/> stanza
  error to the user:

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

  <iq to='[email protected]/orchard' type='error' id='active2'>
    <query xmlns='jabber:iq:privacy'>
      <active name='The Empty Set'/>
    </query>
    <error type='cancel'>
      <item-not-found
          xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    </error>
  </iq>

  In order to decline the use of any active list, the connected
  resource MUST send an empty <active/> element with no 'name'
  attribute.

  Example: Client declines the use of active lists:

  <iq from='[email protected]/orchard' type='set' id='active3'>
    <query xmlns='jabber:iq:privacy'>
      <active/>
    </query>
  </iq>

  Example: Server acknowledges success of declining any active list:

  <iq type='result' id='active3' to='[email protected]/orchard'/>





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10.5.  Managing the Default List

  In order to change its default list (which applies to the user as a
  whole, not only the sending resource), the user MUST send an IQ
  stanza of type "set" with a <query/> element qualified by the
  'jabber:iq:privacy' namespace that contains an empty <default/> child
  element possessing a 'name' attribute whose value is set to the
  desired list name.

  Example: User requests change of default list:

  <iq from='[email protected]/orchard' type='set' id='default1'>
    <query xmlns='jabber:iq:privacy'>
      <default name='special'/>
    </query>
  </iq>

  Example: Server acknowledges success of default list change:

  <iq type='result' id='default1' to='[email protected]/orchard'/>

  If the user attempts to change which list is the default list but the
  default list is in use by at least one connected resource other than
  the sending resource, the server MUST return a <conflict/> stanza
  error to the sending resource:

  Example: Client attempts to change the default list but that list is
  in use by another resource:

  <iq to='[email protected]/orchard' type='error' id='default1'>
    <query xmlns='jabber:iq:privacy'>
      <default name='special'/>
    </query>
    <error type='cancel'>
      <conflict
          xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    </error>
  </iq>

  If the user attempts to set a default list but a list by that name
  does not exist, the server MUST return an <item-not-found/> stanza
  error to the user:









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

  <iq to='[email protected]/orchard' type='error' id='default1'>
    <query xmlns='jabber:iq:privacy'>
      <default name='The Empty Set'/>
    </query>
    <error type='cancel'>
      <item-not-found
          xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    </error>
  </iq>

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

  Example: Client declines the use of the default list:

  <iq from='[email protected]/orchard' type='set' id='default2'>
    <query xmlns='jabber:iq:privacy'>
      <default/>
    </query>
  </iq>

  Example: Server acknowledges success of declining any default list:

  <iq type='result' id='default2' to='[email protected]/orchard'/>

  If one connected resource attempts to decline the use of a default
  list for the user as a whole but the default list currently applies
  to at least one other connected resource, the server MUST return a
  <conflict/> error to the sending resource:

  Example: Client attempts to decline a default list but that list is
  in use by another resource:

  <iq to='[email protected]/orchard' type='error' id='default3'>
    <query xmlns='jabber:iq:privacy'>
      <default/>
    </query>
    <error type='cancel'>
      <conflict
          xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    </error>
  </iq>






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10.6.  Editing a Privacy List

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

  Example: Client edits a privacy list:

  <iq from='[email protected]/orchard' type='set' id='edit1'>
    <query xmlns='jabber:iq:privacy'>
      <list name='public'>
        <item type='jid'
              value='[email protected]'
              action='deny'
              order='3'/>
        <item type='jid'
              value='[email protected]'
              action='deny'
              order='5'/>
        <item action='allow' order='68'/>
      </list>
    </query>
  </iq>

  Example: Server acknowledges success of list edit:

  <iq type='result' id='edit1' to='[email protected]/orchard'/>

  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 "[email protected]" item and the
  "[email protected]" item, the user's client MUST renumber the
  relevant items before submitting the list to the server.

  The server MUST now send a "privacy list push" to all connected
  resources:

  Example: Privacy list push on list edit:

  <iq to='[email protected]/orchard' type='set' id='push1'>
    <query xmlns='jabber:iq:privacy'>
      <list name='public'/>
    </query>
  </iq>



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  <iq to='[email protected]/home' type='set' id='push2'>
    <query xmlns='jabber:iq:privacy'>
      <list name='public'/>
    </query>
  </iq>

  In accordance with the semantics of IQ stanzas defined in
  [XMPP-CORE], each connected resource MUST return an IQ result to the
  server as well:

  Example: Acknowledging receipt of privacy list pushes:

  <iq from='[email protected]/orchard'
      type='result'
      id='push1'/>

  <iq from='[email protected]/home'
      type='result'
      id='push2'/>

10.7.  Adding a New Privacy List

  The same protocol used to edit an existing list is used to create a
  new list.  If the list name matches that of an existing list, the
  request to add a new list will overwrite the old one.  As with list
  edits, the server MUST also send a "privacy list push" to all
  connected resources.

10.8.  Removing a Privacy List

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

  Example: Client removes a privacy list:

  <iq from='[email protected]/orchard' type='set' id='remove1'>
    <query xmlns='jabber:iq:privacy'>
      <list name='private'/>
    </query>
  </iq>

  Example: Server acknowledges success of list removal:

  <iq type='result' id='remove1' to='[email protected]/orchard'/>




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  If a user attempts to remove a list that is currently being applied
  to at least one resource other than the sending resource, the server
  MUST return a <conflict/> stanza error to the user; i.e., the user
  MUST first set another list to active or default before attempting to
  remove it.  If the user attempts to remove a list but a list by that
  name does not exist, the server MUST return an <item-not-found/>
  stanza error to the user.  If the user attempts to remove more than
  one list in the same request, the server MUST return a <bad request/>
  stanza error to the user.

10.9.  Blocking Messages

  Server-side privacy lists enable a user to block incoming messages
  from other entities based on the entity's JID, roster group, or
  subscription status (or globally).  The following examples illustrate
  the protocol.  (Note: For the sake of brevity, IQ stanzas of type
  "result" are not shown in the following examples, nor are "privacy
  list pushes".)

  Example: User blocks based on JID:

  <iq from='[email protected]/orchard' type='set' id='msg1'>
    <query xmlns='jabber:iq:privacy'>
      <list name='message-jid-example'>
        <item type='jid'
              value='[email protected]'
              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 entity with the specified JID.

  Example: User blocks based on roster group:

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



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      </list>
    </query>
  </iq>

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

  Example: User blocks based on subscription type:

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

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

  Example: User blocks globally:

  <iq from='[email protected]/orchard' 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.

10.10.  Blocking Inbound Presence Notifications

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



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

  Example: User blocks based on JID:

  <iq from='[email protected]/orchard' type='set' id='presin1'>
    <query xmlns='jabber:iq:privacy'>
      <list name='presin-jid-example'>
        <item type='jid'
              value='[email protected]'
              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 entity with the
  specified JID.

  Example: User blocks based on roster group:

  <iq from='[email protected]/orchard' 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 entities in the
  specified roster group.








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  Example: User blocks based on subscription type:

  <iq from='[email protected]/orchard' type='set' id='presin3'>
    <query xmlns='jabber:iq:privacy'>
      <list name='presin-sub-example'>
        <item type='subscription'
              value='to'
              action='deny'
              order='9'>
          <presence-in/>
        </item>
      </list>
    </query>
  </iq>

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

  Example: User blocks globally:

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

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

10.11.  Blocking Outbound Presence Notifications

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

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





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  Example: User blocks based on JID:

  <iq from='[email protected]/orchard' type='set' id='presout1'>
    <query xmlns='jabber:iq:privacy'>
      <list name='presout-jid-example'>
        <item type='jid'
              value='[email protected]'
              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 entity with the specified
  JID.

  Example: User blocks based on roster group:

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

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

  Example: User blocks based on subscription type:

  <iq from='[email protected]/orchard' type='set' id='presout3'>
    <query xmlns='jabber:iq:privacy'>
      <list name='presout-sub-example'>
        <item type='subscription'
              value='from'
              action='deny'
              order='17'>
          <presence-out/>



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        </item>
      </list>
    </query>
  </iq>

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

  Example: User blocks globally:

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

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

10.12.  Blocking IQ Stanzas

  Server-side privacy lists enable a user to block incoming IQ stanzas
  from other entities based on the entity's JID, roster group, or
  subscription status (or globally).  The following examples illustrate
  the protocol.

  Example: User blocks based on JID:

  <iq from='[email protected]/orchard' type='set' id='iq1'>
    <query xmlns='jabber:iq:privacy'>
      <list name='iq-jid-example'>
        <item type='jid'
              value='[email protected]'
              action='deny'
              order='29'>
          <iq/>
        </item>
      </list>
    </query>
  </iq>

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



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  Example: User blocks based on roster group:

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

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

  Example: User blocks based on subscription type:

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

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














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  Example: User blocks globally:

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

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

10.13.  Blocking All Communication

  Server-side privacy lists enable a user to block all stanzas from and
  to other entities based on the entity's JID, roster group, or
  subscription status (or globally).  Note that this includes
  subscription-related presence stanzas, which are excluded by Blocking
  Inbound Presence Notifications (Section 10.10).  The following
  examples illustrate the protocol.

  Example: User blocks based on JID:

  <iq from='[email protected]/orchard' type='set' id='all1'>
    <query xmlns='jabber:iq:privacy'>
      <list name='all-jid-example'>
        <item type='jid'
              value='[email protected]'
              action='deny'
              order='23'/>
      </list>
    </query>
  </iq>

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

  Example: User blocks based on roster group:

  <iq from='[email protected]/orchard' type='set' id='all2'>
    <query xmlns='jabber:iq:privacy'>
      <list name='all-group-example'>
        <item type='group'
              value='Enemies'



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              action='deny'
              order='13'/>
      </list>
    </query>
  </iq>

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

  Example: User blocks based on subscription type:

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

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

  Example: User blocks globally:

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

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

10.14.  Blocked Entity Attempts to Communicate with User

  If a blocked entity attempts to send message or presence stanzas to
  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 <service-unavailable/> stanza error, since this is the
  standard error code sent from a client that does not understand the
  namespace of an IQ get or set.  IQ stanzas of other types SHOULD be
  silently dropped by the server.

  Example: Blocked entity attempts to send IQ get:

  <iq type='get'
      to='[email protected]'
      from='[email protected]/pda'
      id='probing1'>
    <query xmlns='jabber:iq:version'/>
  </iq>

  Example: Server returns error to blocked entity:

  <iq type='error'
      from='[email protected]'
      to='[email protected]/pda'
      id='probing1'>
    <query xmlns='jabber:iq:version'/>
    <error type='cancel'>
      <service-unavailable
          xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    </error>
  </iq>

10.15.  Higher-Level Heuristics

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

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

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

  o  allow communications from any user who is in one of the groups
     that make up my roster (i.e., listing each group as a separate
     list item), but block communications from everyone else

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



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

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

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

11.  Server Rules for Handling XML Stanzas

  Basic routing and delivery rules for servers are defined in
  [XMPP-CORE].  This section defines additional rules for
  XMPP-compliant instant messaging and presence servers.

11.1.  Inbound Stanzas

  If the hostname of the domain identifier portion of the JID contained
  in the 'to' attribute of an inbound stanza matches a hostname of the
  server itself and the JID contained in the 'to' attribute is of the
  form <[email protected]> or <[email protected]/resource>, the server
  MUST first apply any privacy lists (Section 10) that are in force,
  then follow the rules defined below:

  1.  If the JID is of the form <user@domain/resource> and an available
      resource matches the full JID, the recipient's server MUST
      deliver the stanza to that resource.

  2.  Else if the JID is of the form <user@domain> or <user@domain/
      resource> and the associated user account does not exist, the
      recipient's server (a) SHOULD silently ignore the stanza (i.e.,
      neither deliver it nor return an error) if it is a presence
      stanza, (b) MUST return a <service-unavailable/> stanza error to
      the sender if it is an IQ stanza, and (c) SHOULD return a
      <service-unavailable/> stanza error to the sender if it is a
      message stanza.

  3.  Else if the JID is of the form <user@domain/resource> and no
      available resource matches the full JID, the recipient's server
      (a) SHOULD silently ignore the stanza (i.e., neither deliver it



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      nor return an error) if it is a presence stanza, (b) MUST return
      a <service-unavailable/> stanza error to the sender if it is an
      IQ stanza, and (c) SHOULD treat the stanza as if it were
      addressed to <user@domain> if it is a message stanza.

  4.  Else if the JID is of the form <user@domain> and there is at
      least one available resource available for the user, the
      recipient's server MUST follow these rules:

      1.  For message stanzas, the server SHOULD deliver the stanza to
          the highest-priority available resource (if the resource did
          not provide a value for the <priority/> element, the server
          SHOULD consider it to have provided a value of zero).  If two
          or more available resources have the same priority, the
          server MAY use some other rule (e.g., most recent connect
          time, most recent activity time, or highest availability as
          determined by some hierarchy of <show/> values) to choose
          between them or MAY deliver the message to all such
          resources.  However, the server MUST NOT deliver the stanza
          to an available resource with a negative priority; if the
          only available resource has a negative priority, the server
          SHOULD handle the message as if there were no available
          resources (defined below).  In addition, the server MUST NOT
          rewrite the 'to' attribute (i.e., it MUST leave it as
          <user@domain> rather than change it to <user@domain/
          resource>).

      2.  For presence stanzas other than those of type "probe", the
          server MUST deliver the stanza to all available resources;
          for presence probes, the server SHOULD reply based on the
          rules defined in Presence Probes (Section 5.1.3).  In
          addition, the server MUST NOT rewrite the 'to' attribute
          (i.e., it MUST leave it as <user@domain> rather than change
          it to <user@domain/resource>).

      3.  For IQ stanzas, the server itself MUST reply on behalf of the
          user with either an IQ result or an IQ error, and MUST NOT
          deliver the IQ stanza to any of the available resources.
          Specifically, if the semantics of the qualifying namespace
          define a reply that the server can provide, the server MUST
          reply to the stanza on behalf of the user; if not, the server
          MUST reply with a <service-unavailable/> stanza error.

  5.  Else if the JID is of the form <user@domain> and there are no
      available resources associated with the user, how the stanza is
      handled depends on the stanza type:





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      1.  For presence stanzas of type "subscribe", "subscribed",
          "unsubscribe", and "unsubscribed", the server MUST maintain a
          record of the stanza and deliver the stanza at least once
          (i.e., when the user next creates an available resource); in
          addition, the server MUST continue to deliver presence
          stanzas of type "subscribe" until the user either approves or
          denies the subscription request (see also Presence
          Subscriptions (Section 5.1.6)).

      2.  For all other presence stanzas, the server SHOULD silently
          ignore the stanza by not storing it for later delivery or
          replying to it on behalf of the user.

      3.  For message stanzas, the server MAY choose to store the
          stanza on behalf of the user and deliver it when the user
          next becomes available, or forward the message to the user
          via some other means (e.g., to the user's email account).
          However, if offline message storage or message forwarding is
          not enabled, the server MUST return to the sender a
          <service-unavailable/> stanza error.  (Note: Offline message
          storage and message forwarding are not defined in XMPP, since
          they are strictly a matter of implementation and service
          provisioning.)

      4.  For IQ stanzas, the server itself MUST reply on behalf of the
          user with either an IQ result or an IQ error.  Specifically,
          if the semantics of the qualifying namespace define a reply
          that the server can provide, the server MUST reply to the
          stanza on behalf of the user; if not, the server MUST reply
          with a <service-unavailable/> stanza error.

11.2.  Outbound Stanzas

  If the hostname of the domain identifier portion of the address
  contained in the 'to' attribute of an outbound stanza matches a
  hostname of the server itself, the server MUST deliver the stanza to
  a local entity according the rules for Inbound Stanzas (Section
  11.1).

  If the hostname of the domain identifier portion of the address
  contained in the 'to' attribute of an outbound stanza does not match
  a hostname of the server itself, the server MUST attempt to route the
  stanza to the foreign domain.  The recommended order of actions is as
  follows:







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  1.  First attempt to resolve the foreign hostname using an [SRV]
      Service of "xmpp-server" and Proto of "tcp", resulting in
      resource records such as "_xmpp-server._tcp.example.com.", as
      specified in [XMPP-CORE].

  2.  If the "xmpp-server" address record resolution fails, attempt to
      resolve the "_im" or "_pres" [SRV] Service as specified in
      [IMP-SRV], using the "_im" Service for <message/> stanzas and the
      "_pres" Service for <presence/> stanzas (it is up to the
      implementation how to handle <iq/> stanzas).  This will result in
      one or more resolutions of the form "_im.<proto>.example.com." or
      "_pres.<proto>.example.com.", where "<proto>" would be a label
      registered in the Instant Messaging SRV Protocol Label registry
      or the Presence SRV Protocol Label registry: either "_xmpp" for
      an XMPP-aware domain or some other IANA-registered label (e.g.,
      "_simple") for a non-XMPP-aware domain.

  3.  If both SRV address record resolutions fail, attempt to perform a
      normal IPv4/IPv6 address record resolution to determine the IP
      address using the "xmpp-server" port of 5269 registered with the
      IANA, as specified in [XMPP-CORE].

  Administrators of server deployments are strongly encouraged to keep
  the _im._xmpp, _pres._xmpp, and _xmpp._tcp SRV records properly
  synchronized, since different implementations might perform the "_im"
  and "_pres" lookups before the "xmpp-server" lookup.

12.  IM and Presence Compliance Requirements

  This section summarizes the specific aspects of the Extensible
  Messaging and Presence Protocol that MUST be supported by instant
  messaging and presence servers and clients in order to be considered
  compliant implementations.  All such applications MUST comply with
  the requirements specified in [XMPP-CORE].  The text in this section
  specifies additional compliance requirements for instant messaging
  and presence servers and clients; note well that the requirements
  described here supplement but do not supersede the core requirements.
  Note also that a server or client MAY support only presence or
  instant messaging, and is not required to support both if only a
  presence service or an instant messaging service is desired.

12.1.  Servers

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





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  o  All server-related instant messaging and presence syntax and
     semantics defined in this document, including presence broadcast
     on behalf of clients, presence subscriptions, roster storage and
     manipulation, privacy lists, and IM-specific routing and delivery
     rules

12.2.  Clients

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

  o  Generation and handling of the IM-specific semantics of XML
     stanzas as defined by the XML schemas, including the 'type'
     attribute of message and presence stanzas as well as their child
     elements

  o  All client-related instant messaging syntax and semantics defined
     in this document, including presence subscriptions, roster
     management, and privacy lists

  o  End-to-end object encryption as defined in End-to-End Object
     Encryption in the Extensible Messaging and Presence Protocol
     (XMPP) [XMPP-E2E]

  A client MUST also handle addresses that are encoded as "im:" URIs as
  specified in [CPIM], and MAY do so by removing the "im:" scheme and
  entrusting address resolution to the server as specified under
  Outbound Stanzas (Section 11.2).

13.  Internationalization Considerations

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

14.  Security Considerations

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

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








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  o  When a server processes an inbound stanza of any kind whose
     intended recipient is a user associated with one of the server's
     hostnames, the server MUST first apply any privacy lists (Section
     10) that are in force (see Server Rules for Handling XML Stanzas
     (Section 11)).

  o  When a server processes an inbound presence stanza of type "probe"
     whose intended recipient is a user associated with one of the
     server's hostnames, the server MUST NOT reveal the user's presence
     information if the sender is an entity that is not authorized to
     receive that information as determined by presence subscriptions
     (see Client and Server Presence Responsibilities (Section 5.1)).

  o  When a server processes an outbound presence stanza with no type
     or of type "unavailable", it MUST follow the rules defined under
     Client and Server Presence Responsibilities (Section 5.1) in order
     to ensure that such presence information is not broadcasted to
     entities that are not authorized to know such information.

  o  When a server generates an error stanza in response to receiving a
     stanza for a user who does not exist, the use of the
     <service-unavailable/> error condition helps protect against
     well-known dictionary attacks, since this is the same error
     condition that is returned if, for instance, the namespace of an
     IQ child element is not understood, or if offline message storage
     or message forwarding is not enabled for a domain.

15.  IANA Considerations

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

15.1.  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.  (This
  namespace name adheres to the format defined in The IETF XML Registry
  [XML-REG].)

  URI: urn:ietf:params:xml:ns:xmpp-session
  Specification: RFC 3921
  Description: This is the XML namespace name for session-related data
     in the Extensible Messaging and Presence Protocol (XMPP) as
     defined by RFC 3921.
  Registrant Contact: IETF, XMPP Working Group, <[email protected]>






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15.2.  Instant Messaging SRV Protocol Label Registration

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

  Protocol label: _xmpp
  Specification: RFC 3921
  Description: Instant messaging protocol label for the Extensible
     Messaging and Presence Protocol (XMPP) as defined by RFC 3921.
  Registrant Contact: IETF, XMPP Working Group, <[email protected]>

15.3.  Presence SRV Protocol Label Registration

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

  Protocol label: _xmpp
  Specification: RFC 3921
  Description: Presence protocol label for the Extensible Messaging and
     Presence Protocol (XMPP) as defined by RFC 3921.
  Registrant Contact: IETF, XMPP Working Group, <[email protected]>

16.  References

16.1.  Normative References

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

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

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

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

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



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  [XML]       Bray, T., Paoli, J., Sperberg-McQueen, C., and E. Maler,
              "Extensible Markup Language (XML) 1.0 (2nd ed)", W3C
              REC-xml, October 2000, <http://www.w3.org/TR/REC-xml>.

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

  [XMPP-CORE] Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 3920, October 2004.

  [XMPP-E2E]  Saint-Andre, P., "End-to-End Object Encryption in the
              Extensible Messaging and Presence Protocol (XMPP)", RFC
              3923, October 2004.

16.2.  Informative References

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

  [IRC]       Oikarinen, J. and D. Reed, "Internet Relay Chat
              Protocol", RFC 1459, May 1993.

  [JEP-0054]  Saint-Andre, P., "vcard-temp", JSF JEP 0054, March 2003.

  [JEP-0077]  Saint-Andre, P., "In-Band Registration", JSF JEP 0077,
              August 2004.

  [JEP-0078]  Saint-Andre, P., "Non-SASL Authentication", JSF JEP 0078,
              July 2004.

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

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

  [XML-REG]   Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.












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Appendix A.  vCards

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

Appendix B.  XML Schemas

  The following XML schemas are descriptive, not normative.  For
  schemas defining the core features of XMPP, refer to [XMPP-CORE].

B.1  jabber:client

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

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

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

    <xs:element name='message'>
       <xs:complexType>
          <xs:sequence>
            <xs:choice minOccurs='0' maxOccurs='unbounded'>
              <xs:element ref='subject'/>
              <xs:element ref='body'/>
              <xs:element ref='thread'/>
            </xs:choice>
            <xs:any     namespace='##other'
                        minOccurs='0'
                        maxOccurs='unbounded'/>
            <xs:element ref='error'
                        minOccurs='0'/>











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          </xs:sequence>
          <xs:attribute name='from'
                        type='xs:string'
                        use='optional'/>
          <xs:attribute name='id'
                        type='xs:NMTOKEN'
                        use='optional'/>
          <xs:attribute name='to'
                        type='xs:string'
                        use='optional'/>
          <xs:attribute name='type' use='optional' default='normal'>
            <xs:simpleType>
              <xs:restriction base='xs:NCName'>
                <xs:enumeration value='chat'/>
                <xs:enumeration value='error'/>
                <xs:enumeration value='groupchat'/>
                <xs:enumeration value='headline'/>
                <xs:enumeration value='normal'/>
              </xs:restriction>
            </xs:simpleType>
          </xs:attribute>
          <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
    </xs:element>

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

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

    <xs:element name='thread' type='xs:NMTOKEN'/>

    <xs:element name='presence'>



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

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



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    </xs:element>

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

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

    <xs:element name='iq'>
      <xs:complexType>
        <xs:sequence>
          <xs:any     namespace='##other'
                      minOccurs='0'/>
          <xs:element ref='error'
                      minOccurs='0'/>
        </xs:sequence>
        <xs:attribute name='from'
                      type='xs:string'
                      use='optional'/>
        <xs:attribute name='id'
                      type='xs:NMTOKEN'
                      use='required'/>
        <xs:attribute name='to'
                      type='xs:string'
                      use='optional'/>
        <xs:attribute name='type' use='required'>
          <xs:simpleType>
            <xs:restriction base='xs:NCName'>
              <xs:enumeration value='error'/>
              <xs:enumeration value='get'/>
              <xs:enumeration value='result'/>
              <xs:enumeration value='set'/>
            </xs:restriction>
          </xs:simpleType>
        </xs:attribute>
        <xs:attribute ref='xml:lang' use='optional'/>
      </xs:complexType>
    </xs:element>

    <xs:element name='error'>
      <xs:complexType>
        <xs:sequence  xmlns:err='urn:ietf:params:xml:ns:xmpp-stanzas'>



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          <xs:group   ref='err:stanzaErrorGroup'/>
          <xs:element ref='err:text'
                      minOccurs='0'/>
        </xs:sequence>
        <xs:attribute name='code' type='xs:byte' use='optional'/>
        <xs:attribute name='type' use='required'>
          <xs:simpleType>
            <xs:restriction base='xs:NCName'>
              <xs:enumeration value='auth'/>
              <xs:enumeration value='cancel'/>
              <xs:enumeration value='continue'/>
              <xs:enumeration value='modify'/>
              <xs:enumeration value='wait'/>
            </xs:restriction>
          </xs:simpleType>
        </xs:attribute>
      </xs:complexType>
    </xs:element>

  </xs:schema>

B.2  jabber:server

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

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

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

    <xs:element name='message'>
       <xs:complexType>
          <xs:sequence>
            <xs:choice minOccurs='0' maxOccurs='unbounded'>
              <xs:element ref='subject'/>
              <xs:element ref='body'/>
              <xs:element ref='thread'/>
            </xs:choice>
            <xs:any     namespace='##other'
                        minOccurs='0'
                        maxOccurs='unbounded'/>
            <xs:element ref='error'
                        minOccurs='0'/>
          </xs:sequence>




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          <xs:attribute name='from'
                        type='xs:string'
                        use='required'/>
          <xs:attribute name='id'
                        type='xs:NMTOKEN'
                        use='optional'/>
          <xs:attribute name='to'
                        type='xs:string'
                        use='required'/>
          <xs:attribute name='type' use='optional' default='normal'>
            <xs:simpleType>
              <xs:restriction base='xs:NCName'>
                <xs:enumeration value='chat'/>
                <xs:enumeration value='error'/>
                <xs:enumeration value='groupchat'/>
                <xs:enumeration value='headline'/>
                <xs:enumeration value='normal'/>
              </xs:restriction>
            </xs:simpleType>
          </xs:attribute>
          <xs:attribute ref='xml:lang' use='optional'/>
       </xs:complexType>
    </xs:element>

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

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

    <xs:element name='thread' type='xs:NMTOKEN'/>

    <xs:element name='presence'>
      <xs:complexType>



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

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



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

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

    <xs:element name='iq'>
      <xs:complexType>
        <xs:sequence>
          <xs:any     namespace='##other'
                      minOccurs='0'/>
          <xs:element ref='error'
                      minOccurs='0'/>
        </xs:sequence>
        <xs:attribute name='from'
                      type='xs:string'
                      use='required'/>
        <xs:attribute name='id'
                      type='xs:NMTOKEN'
                      use='required'/>
        <xs:attribute name='to'
                      type='xs:string'
                      use='required'/>
        <xs:attribute name='type' use='required'>
          <xs:simpleType>
            <xs:restriction base='xs:NCName'>
              <xs:enumeration value='error'/>
              <xs:enumeration value='get'/>
              <xs:enumeration value='result'/>
              <xs:enumeration value='set'/>
            </xs:restriction>
          </xs:simpleType>
        </xs:attribute>
        <xs:attribute ref='xml:lang' use='optional'/>
      </xs:complexType>
    </xs:element>

    <xs:element name='error'>
      <xs:complexType>
        <xs:sequence  xmlns:err='urn:ietf:params:xml:ns:xmpp-stanzas'>
          <xs:group   ref='err:stanzaErrorGroup'/>
          <xs:element ref='err:text'



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                      minOccurs='0'/>
        </xs:sequence>
        <xs:attribute name='code' type='xs:byte' use='optional'/>
        <xs:attribute name='type' use='required'>
          <xs:simpleType>
            <xs:restriction base='xs:NCName'>
              <xs:enumeration value='auth'/>
              <xs:enumeration value='cancel'/>
              <xs:enumeration value='continue'/>
              <xs:enumeration value='modify'/>
              <xs:enumeration value='wait'/>
            </xs:restriction>
          </xs:simpleType>
        </xs:attribute>
      </xs:complexType>
    </xs:element>

  </xs:schema>

B.3  session

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

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

    <xs:element name='session' type='empty'/>

    <xs:simpleType name='empty'>
      <xs:restriction base='xs:string'>
        <xs:enumeration value=''/>
      </xs:restriction>
    </xs:simpleType>

  </xs:schema>

B.4  jabber:iq:privacy

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

  <xs:schema
      xmlns:xs='http://www.w3.org/2001/XMLSchema'
      targetNamespace='jabber:iq:privacy'





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      xmlns='jabber:iq:privacy'
      elementFormDefault='qualified'>

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

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

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

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



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

    <xs:element name='item'>
      <xs:complexType>
        <xs:sequence>
          <xs:element name='iq'
                      minOccurs='0'
                      type='empty'/>
          <xs:element name='message'
                      minOccurs='0'
                      type='empty'/>
          <xs:element name='presence-in'
                      minOccurs='0'
                      type='empty'/>
          <xs:element name='presence-out'
                      minOccurs='0'
                      type='empty'/>
        </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:unsignedInt'
                      use='required'/>
        <xs:attribute name='type' use='optional'>
          <xs:simpleType>
            <xs:restriction base='xs:NCName'>
              <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>




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    <xs:simpleType name='empty'>
      <xs:restriction base='xs:string'>
        <xs:enumeration value=''/>
      </xs:restriction>
    </xs:simpleType>

  </xs:schema>

B.5  jabber:iq:roster

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

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

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

    <xs:element name='item'>
      <xs:complexType>
        <xs:sequence>
          <xs:element ref='group'
                      minOccurs='0'
                      maxOccurs='unbounded'/>
        </xs:sequence>
        <xs:attribute name='ask' use='optional'>
          <xs:simpleType>
            <xs:restriction base='xs:NCName'>
              <xs:enumeration value='subscribe'/>
            </xs:restriction>
          </xs:simpleType>
        </xs:attribute>
        <xs:attribute name='jid' type='xs:string' use='required'/>
        <xs:attribute name='name' type='xs:string' use='optional'/>
        <xs:attribute name='subscription' use='optional'>
          <xs:simpleType>
            <xs:restriction base='xs:NCName'>




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              <xs:enumeration value='both'/>
              <xs:enumeration value='from'/>
              <xs:enumeration value='none'/>
              <xs:enumeration value='remove'/>
              <xs:enumeration value='to'/>
            </xs:restriction>
          </xs:simpleType>
        </xs:attribute>
      </xs:complexType>
    </xs:element>

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

  </xs:schema>

Appendix C.  Differences Between Jabber IM/Presence Protocols and XMPP

  This section is non-normative.

  XMPP has been adapted from the protocols originally developed in the
  Jabber open-source community, which can be thought of as "XMPP 0.9".
  Because there exists a large installed base of Jabber implementations
  and deployments, it may be helpful to specify the key differences
  between the relevant Jabber protocols and XMPP in order to expedite
  and encourage upgrades of those implementations and deployments to
  XMPP.  This section summarizes the differences that relate
  specifically to instant messaging and presence applications, while
  the corresponding section of [XMPP-CORE] summarizes the differences
  that relate to all XMPP applications.

C.1  Session Establishment

  The client-to-server authentication protocol developed in the Jabber
  community assumed that every client is an IM client and therefore
  initiated an IM session upon successful authentication and resource
  binding, which are performed simultaneously (documentation of this
  protocol is contained in [JEP-0078], published by the Jabber Software
  Foundation [JSF]).  XMPP maintains a stricter separation between core
  functionality and IM functionality; therefore, an IM session is not
  created until the client specifically requests one using the protocol
  defined under Session Establishment (Section 3).










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C.2  Privacy Lists

  The Jabber community began to define a protocol for communications
  blocking (privacy lists) in late 2001, but that effort was deprecated
  once the XMPP Working Group was formed.  Therefore the protocol
  defined under Blocking Communication (Section 10) is the only such
  protocol defined for use in the Jabber community.

Contributors

  Most of the core aspects of the Extensible Messaging and Presence
  Protocol were developed originally within the Jabber open-source
  community in 1999.  This community was founded by Jeremie Miller, who
  released source code for the initial version of the jabberd server in
  January 1999.  Major early contributors to the base protocol also
  included Ryan Eatmon, Peter Millard, Thomas Muldowney, and Dave
  Smith.  Work specific to instant messaging and presence by the XMPP
  Working Group has concentrated especially on IM session establishment
  and communication blocking (privacy lists); the session establishment
  protocol was mainly developed by Rob Norris and Joe Hildebrand, and
  the privacy lists protocol was originally contributed by Peter
  Millard.

Acknowledgements

  Thanks are due to a number of individuals in addition to the
  contributors listed.  Although it is difficult to provide a complete
  list, the following individuals were particularly helpful in defining
  the protocols or in commenting on the specifications in this memo:
  Thomas Charron, Richard Dobson, Schuyler Heath, Jonathan Hogg, Craig
  Kaes, Jacek Konieczny, Lisa Dusseault, Alexey Melnikov, Keith
  Minkler, Julian Missig, Pete Resnick, Marshall Rose, Jean-Louis
  Seguineau, Alexey Shchepin, Iain Shigeoka, and David Waite.  Thanks
  also to members of the XMPP Working Group and the IETF community for
  comments and feedback provided throughout the life of this memo.

Author's Address

  Peter Saint-Andre (editor)
  Jabber Software Foundation

  EMail: [email protected]









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Full Copyright Statement

  Copyright (C) The Internet Society (2004).

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

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

Intellectual Property

  The IETF takes no position regarding the validity or scope of any
  Intellectual Property Rights or other rights that might be claimed to
  pertain to the implementation or use of the technology described in
  this document or the extent to which any license under such rights
  might or might not be available; nor does it represent that it has
  made any independent effort to identify any such rights.  Information
  on the IETF's procedures with respect to rights in IETF Documents can
  be found in BCP 78 and BCP 79.

  Copies of IPR disclosures made to the IETF Secretariat and any
  assurances of licenses to be made available, or the result of an
  attempt made to obtain a general license or permission for the use of
  such proprietary rights by implementers or users of this
  specification can be obtained from the IETF on-line IPR repository at
  http://www.ietf.org/ipr.

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

Acknowledgement

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







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