Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence
draft-saintandre-rfc3921bis-03

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Copyright Notice

Copyright © The IETF Trust (2007).

Abstract

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

This document obsoletes RFC 3921.

Table of Contents

1.  Introduction
    1.1.  Overview
    1.2.  Requirements
    1.3.  Typical Session Flow
    1.4.  Conventions
2.  Managing the Roster
    2.1.  Syntax and Semantics
    2.2.  Retrieving the Roster on Login
    2.3.  Adding a Roster Item
    2.4.  Updating a Roster Item
    2.5.  Deleting a Roster Item
3.  Managing Presence Subscriptions
    3.1.  Requesting a Subscription
    3.2.  Cancelling a Subscription
    3.3.  Unsubscribing
4.  Exchanging Presence Information
    4.1.  Overview
    4.2.  Initial Presence
    4.3.  Presence Probes
    4.4.  Subsequent Presence Broadcast
    4.5.  Unavailable Presence
    4.6.  Directed Presence
    4.7.  Presence Syntax
5.  Exchanging Messages
    5.1.  Attributes
    5.2.  Child Elements
    5.3.  Extended Content
6.  Exchanging IQ Stanzas
7.  A Sample Session
8.  Server Rules for Processing XML Stanzas
    8.1.  No Such User
    8.2.  Full JID at Local Domain
    8.3.  Bare JID at Local Domain
    8.4.  Foreign Domain
9.  IM and Presence Compliance Requirements
    9.1.  Servers
    9.2.  Clients
10.  Internationalization Considerations
11.  Security Considerations
12.  IANA Considerations
    12.1.  Instant Messaging SRV Protocol Label Registration
    12.2.  Presence SRV Protocol Label Registration
13.  References
    13.1.  Normative References
    13.2.  Informative References
Appendix A.  Subscription States
    A.1.  Defined States
    A.2.  Server Processing of Outbound Presence Subscription Stanzas
    A.3.  Server Processing of Inbound Presence Subscription Stanzas
Appendix B.  Blocking Communication
Appendix C.  vCards
Appendix D.  XML Schemas
    D.1.  jabber:client
    D.2.  jabber:server
    D.3.  jabber:iq:roster
Appendix E.  Differences From RFC 3921
Appendix F.  Copying Conditions
§  Index
§  Author's Address
§  Intellectual Property and Copyright Statements

1.  Introduction

1.1.  Overview

The Extensible Messaging and Presence Protocol (XMPP) is a technology for streaming Extensible Markup Language (Paoli, J., Maler, E., Sperberg-McQueen, C., Yergeau, F., and T. Bray, “Extensible Markup Language (XML) 1.0 (Fourth Edition),” August 2006.) [XML] elements in order to exchange messages, presence information, and other structured data in close to real time. The core features of XMPP are defined in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.). These features -- mainly XML streams, use of Transport Layer Security ([TLS] (Dierks, T. and E. Rescorla, “The Transport Layer Security (TLS) Protocol Version 1.1,” April 2006.)) and Simple Authentication and Security Layer ([SASL] (Melnikov, A. and K. Zeilenga, “Simple Authentication and Security Layer (SASL),” June 2006.)), 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 (see [XML‑NAMES] (Bray, T., Hollander, D., and A. Layman, “Namespaces in XML,” January 1999.)). This document describes extensions to the core features of XMPP that provide the basic functionality expected of an instant messaging (IM) and presence application as defined in [IMP‑REQS] (Day, M., Aggarwal, S., and J. Vincent, “Instant Messaging / Presence Protocol Requirements,” February 2000.).

This document obsoletes RFC 3921.

1.2.  Requirements

Traditionally, instant messaging applications have combined the following factors:

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

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

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

Detailed definitions of these functionality areas are contained in [IMP‑REQS] (Day, M., Aggarwal, S., and J. Vincent, “Instant Messaging / Presence Protocol Requirements,” February 2000.), and the interested reader should refer to that document regarding the requirements addressed herein. While the XMPP instant messaging and presence extensions specified herein meet the requirements of [IMP‑REQS] (Day, M., Aggarwal, S., and J. Vincent, “Instant Messaging / Presence Protocol Requirements,” February 2000.), they were not designed explicitly with that specification in mind, since the base protocol evolved through an open development process within the Jabber open-source community before RFC 2779 was written. Although XMPP protocol extensions addressing many other functionality areas have been defined in the XMPP Standards Foundation's XEP series (e.g., multi-user text chat as specified in [XEP‑0045] (Saint-Andre, P., “Multi-User Chat,” April 2007.)), such extensions are not included in this document because they are not required by [IMP‑REQS] (Day, M., Aggarwal, S., and J. Vincent, “Instant Messaging / Presence Protocol Requirements,” February 2000.).

Note: [IMP‑REQS] (Day, M., Aggarwal, S., and J. Vincent, “Instant Messaging / Presence Protocol Requirements,” February 2000.) stipulates that presence services must be separable from instant messaging services and vice-versa; i.e., it must be possible to use the protocol to provide a presence service, an instant messaging service, or both. Although the text of this document assumes that implementations and deployments will want to offer a unified instant messaging and presence service, there is no requirement that a service must offer both a presence service and an instant messaging service, and the protocol makes it possible to offer separate and distinct services for presence and for instant messaging. (For example, a presence-only service could return <service-unavailable/> errors if clients attempt to send <message/> stanzas.)

1.3.  Typical Session Flow

[XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.) specifies how an XMPP client connects to an XMPP server. In particular, it specifies the preconditions (including XML stream establishment, authentication, and binding of a resource to the stream) that must be fulfilled before a client is allowed to send XML stanzas (the basic unit of meaning in XMPP) to other entities on an XMPP network. The reader is referred to [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.) for details, and knowledge of [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.) is assumed herein.

Upon fulfillment of the preconditions specified in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.), an XMPP client has a long-lived XML stream with an XMPP server, which enables the user to send and receive a potentially unlimited number of XML stanzas over the stream. Such a stream can be used as the basis for the exchange of instant messaging, presence, and other information in close to real time. The typical flow for an instant messaging and presence session is as follows:

1. Negotiate an XML stream with one's server. (See [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.).)
2. Retrieve one's roster. (See Section 2.2 (Retrieving the Roster on Login).)
3. Send initial presence to the server for broadcasting to all subscribed contacts, thus "going online" from the perspective of XMPP communications. (See Section 4.2 (Initial Presence).)
4. Exchange messages, manage presence subscriptions, perform roster updates, and in general process and generate other XML stanzas with particular semantics throughout the life of the session. (See Section 5 (Exchanging Messages) and Section 6 (Exchanging IQ Stanzas).)
5. Terminate the session when desired by sending unavailable presence and closing the underlying XML stream. (See Section 4.5 (Unavailable Presence).)

1.4.  Conventions

This document inherits the terminology defined in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.).

The following keywords are to be interpreted as described in [TERMS] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.): "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".

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

In examples, lines have been wrapped for improved readability, "[...]" means elision, and the following prepended strings are used:

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

2.  Managing the Roster

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

2.1.  Syntax and Semantics

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

2.1.1.  Items

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

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

1. The 'jid' attribute is REQUIRED; the value of this attribute is a unique identifier or "key" for each roster item is a Jabber Identifier or JID. (Note: When the item added represents another IM user, the value of the 'jid' attribute MUST be a bare JID <contact@domain> rather a full JID <contact@domain/resource>, since the desired result is for the user to receive presence from all of the contact's resources, not merely the particular resource specified in the 'to' attribute.)
2. The 'name' attribute is OPTIONAL; the value of this attribute specifies the "handle" to be associated with the JID, as determined by the user (not the contact). The value of the 'name' attribute is opaque to the server but may have meaning to a human user.
3. The 'subscription' attribute is OPTIONAL; see Section 2.1.3 (Subscription Attribute).
4. The 'ask' attribute is OPTIONAL and is used to specify certain subscription sub-states; for details, see Section 3.1.2 (Server Processing of Outbound Subscription Request).
5. The <group/> element is OPTIONAL; the XML character of this element specifies a category into which the roster item should be grouped by a client. The <item/> MAY more than one <group/> element. The XML character data of the <group/> element has no meaning to the server but may have meaning to a human user.

2.1.2.  Actions

2.1.2.1.  Roster Get

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

The <query/> element in a roster get MUST NOT contain any <item/> child elements.

2.1.2.2.  Roster Set

A ROSTER SET is an IQ stanza of type "set" sent from client to server and containing a <query/> element qualified by the 'jabber:iq:roster' namespace.

The following rules apply to roster sets:

1. The <query/> element MUST contain one and only one <item/> element.
2. A receiving server MUST ignore any value of the 'subscription' attribute other than "remove" (see Section 2.1.3 (Subscription Attribute)).
3. A receiving server MUST ignore any 'to' address specified on the IQ stanza and MUST handle the IQ stanza as if it included no 'to' attribute.

2.1.2.3.  Roster Push

A ROSTER PUSH is an IQ stanza of type "set" sent from server to client and containing a <query/> element qualified by the 'jabber:iq:roster' namespace.

The following rules apply to roster pushes:

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

2.1.2.4.  Roster Result

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

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

2.1.3.  Subscription Attribute

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

• "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
• "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
• "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
• "both" -- both the user and the contact have subscriptions to each other's presence information (also called a "mutual subscription")

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

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

2.2.  Retrieving the Roster on Login

Upon authenticating with a server and binding a resource (thus becoming a connected resource), a client SHOULD request the roster before sending initial presence (however, because receiving the roster may not be desirable for all resources, e.g., a connection with limited bandwidth, the client's request for the roster is recommended and not required). After a connected resource sends initial presence (see Section 4.2 (Initial Presence)), it is referred to as an available resource. If a connected resource requests the roster but does not send initial presence, the server SHOULD NOT send it presence subscriptions and SHOULD NOT send it associated roster pushes. If an available resource does not request the roster during a session, the server SHOULD NOT send it presence subscriptions and MUST NOT associated roster pushes. For the sake of brevity, the term INTERESTED RESOURCE is used herein to refer to the concept of "an available resource that has requested the roster".

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

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

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

If the server cannot process the roster get, it MUST return an appropriate stanza error as described in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.) (such as <service-unavailable/> if the roster namespace is not supported or <internal-server-error/> if the server experiences trouble returning the roster).

2.3.  Adding a Roster Item

2.3.1.  Success Case

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

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

If the server can successfully process the roster set (i.e., if none of the error cases occurs), it MUST create the roster item in persistent storage and send a roster push to all of the user's interested resources containing the new roster item.

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

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

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

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

As required by the semantics of the IQ stanza kind as defined in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.), each resource that received the roster push MUST reply with an IQ stanza of type "result" (or "error").

C: <iq from='juliet@example.com/balcony'
      type='result'
      id='a78b4q6ha463'/>
C: <iq from='juliet@example.com/chamber'
      type='result'
      id='a78b4q6ha464'/>

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

2.3.2.  Error Cases

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

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

1. The <query/> element contains more than one <item/> child element.
2. The <item/> element contains more than one <group/> element, but there are duplicates among the XML character data of each <group/> element (where duplicates are determined using the Resourceprep profile of stringprep as defined in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.)).

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

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

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

Error: Roster set contains more than one item

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

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

Error: Roster set contains item with oversized handle

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

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

Error: Roster set contains duplicate groups

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

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

Error: Roster set contains empty group

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

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

Error: Roster set contains oversized group

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

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

The server MUST return a <not-allowed/> error to the client if the value of the <item/> element's 'jid' attribute matches the bare JID <node@domain> portion of the <iq/> element's 'from' attribute.

Error: Roster set contains sender's JID

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

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

2.4.  Updating a Roster Item

2.4.1.  Success Case

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

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

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

Consider a roster item that is defined as follows:

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

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

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

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

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

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

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

The user may then want to remove the handle altogether (note: including an empty 'name' attribute is equivalent to including no 'name' attribute).

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

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

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

As with adding a roster item, when updating a roster item the server MUST update the roster information in persistent storage, send a roster push to all of the user's interested resources, and send an IQ result to the initiating resource; for details, see Section 2.3 (Adding a Roster Item).

2.4.2.  Error Cases

The error cases described under Section 2.3 (Adding a Roster Item) also apply to updating a roster item.

2.5.  Deleting a Roster Item

2.5.1.  Success Case

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

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

As with adding a roster item, if the server can successfully process the roster set then it MUST update the roster information in persistent storage, send a roster push to all of the user's interested resources (with the 'subscription' attribute set to a value of "remove"), and send an IQ result to the initiating resource; for details, see Section 2.3 (Adding a Roster Item).

The server MUST also generate a presence stanza of type "unsubscribe" and a presence stanza of type "unsubscribed" from the user to the contact.

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

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

2.5.2.  Error Cases

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

Error: Roster item not found

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

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

3.  Managing Presence Subscriptions

In order to protect the privacy of instant messaging users, presence information is disclosed only to other entities that the 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. An entity that has a subscription to a user's presence (or to which a user has a presence subscription) is called a CONTACT. A subscription lasts across sessions; indeed, it lasts until the contact unsubscribes or the user cancels the previously-granted subscription.

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

Note: When a user or contact generates a presence stanza of type "subscribe", "subscribed", "unsubscribe", and "unsubscribed" or a server processes or generates such a stanza on behalf of a user or contact, the server MUST stamp the outgoing presence stanza with the bare JID <node@domain> of the user or contact, not the full JID <node@domain/resource>. This rule helps to prevent presence leaks; for details, see the security considerations of [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.).)

3.1.  Requesting a Subscription

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

3.1.1.  Client Generation of Outbound Subscription Request

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

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

Typically the user's client prompts the user for information about the potential contact ("handle" and desired roster group) and generates a roster set with that information before sending the subscription request, but that behavior is recommended rather than required.

3.1.2.  Server Processing of Outbound Subscription Request

As mentioned, the user's server MUST stamp the outbound subscription request with the bare JID <user@domain> of the user.

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

If the potential contact is hosted on the same server, the server MUST adhere to the rules specified in the next section in processing the subscription request and delivering it to the (local) contact.

If the potential contact is hosted on a different server, the user's server then routes the stanza to that foreign domain in accordance with core XMPP stanza processing rules.

The user's server MUST then send a roster push to all of the user's interested resources, containing the potential contact with a subscription state of "none" and with notation that the subscription is pending (via an 'ask' attribute whose value is "subscribe").

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

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

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

3.1.3.  Server Processing of Inbound Subscription Request

The contact's server MUST adhere to the following rules when processing the inbound subscription request:

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

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

3. If the contact exists and the user already has a subscription to the user's presence, the contact's server SHOULD auto-reply on behalf of the user by sending a presence stanza of type "subscribed" from the contact's bare JID to the user's bare JID.
4. If the contact exists, the user does not already have a subscription to the contact's presence, and there is at least one interested resource associated with the contact when the subscription request is received by the contact's server, the contact's server MUST broadcast that subscription request to all interested resources in accordance with Server Rules for Processing XML Stanzas (Server Rules for Processing XML Stanzas).
5. If the contact exists, the user does not already have a subscription to the contact's presence, and the contact has no interested resources when the subscription request is received by the contact's server, the contact's server MUST keep a record of the complete presence stanza comprising the subscription request, including any extended content contained therein, and deliver the request when the contact next has an interested resource, until the contact either approves or denies the request. (Note: The contact's server MUST NOT deliver more than one subscription request from any given user when the contact next has an interested resource; e.g., if the user sends multiple subscription requests to the contact while the contact is offline, the contact's server SHOULD store only one of those requests, such as the first request or last request, and MUST deliver only one of the requests when the contact next has an interested resource; this helps to prevent "subscription request spam".)

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

3.1.4.  Client Processing of Inbound Subscription Request

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

A subscription request is approved by sending a presence stanza of type "subscribed".

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

Note: Server processing of presence stanzas of type 'subscribed' is described in the following sections for both the contact's server and the user's server.

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

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

Note: Server processing of presence stanzas of type 'unsubscribed' is described under Section 3.2 (Cancelling a Subscription) for both the contact's server and the user's server.

3.1.5.  Server Processing of Outbound Subscription Approval

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

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

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

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

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

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

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

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

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

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

3.1.6.  Server Processing of Inbound Subscription Approval

When the user's server receives the subscription approval, it MUST first check if the contact is in the user's roster with a subscription='none' or subscription='from' and the 'ask' flag set to "subscribe" (i.e., a Appendix A (Subscription States) of "None + Pending Out" or "From + Pending Out"). 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 foregoing check is successful, the user's server MUST initiate a roster push to all of the user's interested resources, containing an updated roster item for the contact with the 'subscription' attribute set to a value of "to".

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

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

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

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

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

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

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

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

3.2.  Cancelling a Subscription

3.2.1.  Client Generation of Subscription Cancellation

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

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

3.2.2.  Server Processing of Outbound Subscription Cancellation

As mentioned, the contact's server MUST stamp the outbound subscription cancellation with the bare JID <user@domain> of the contact.

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

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

If the user is hosted on a different server, the contact's server then routes the stanza to that foreign domain in accordance with core XMPP stanza processing rules.

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

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

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

3.2.3.  Server Processing of Inbound Subscription Cancellation

When the user's server receives the inbound subscription cancellation, it MUST modify the subscription state and send a roster push to the user's interested resource(s).

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

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

3.3.  Unsubscribing

3.3.1.  Client Generation of Unsubscribe

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

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

3.3.2.  Server Processing of Outbound Unsubscribe

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

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

If the contact is hosted on the same server, the server MUST adhere to the rules specified in the next section when processing the unsubscribe.

If the contact is hosted on a different server, the user's server then routes the stanza to that foreign domain in accordance with core XMPP stanza processing rules.

The user's server then MUST send a roster push with the updated roster item to all of the user's interested resources.

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

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

3.3.3.  Server Processing of Inbound Unsubscribe

When the contact's server receives the inbound unsubscribe, it MUST modify the subscription state and send a roster push to the contact's interested resource(s).

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

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

4.  Exchanging Presence Information

4.1.  Overview

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

XMPP presence typically follows a "publish-subscribe" or "observer" pattern, wherein an entity sends presence information to its server, and its server then broadcasts that information to all of the entity's contacts who have a subscription to the entity's presence (in the terminology of [IMP‑MODEL] (Day, M., Rosenberg, J., and H. Sugano, “A Model for Presence and Instant Messaging,” February 2000.), an entity that generates presence information is a "presentity" and the entities that receive presence information are "subscribers"). A client generates presence for broadcasting to all subscribed entities by sending a presence stanza to its server with no 'to' address, where the presence stanza has either no 'type' attribute or a 'type' attribute whose value is "unavailable". This type of presence is called BROADCASTED PRESENCE. (A client MAY also send DIRECTED PRESENCE, i.e., a presence stanza with a 'to' address; this is less common but is sometimes used to send presence to entities that are not subscribed to the principal's presence.)

After a client completes the preconditions specified in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.), it can establish a PRESENCE SESSION at its server by sending initial presence (Initial Presence). Such a presence session is terminated by sending unavailable presence (Unavailable Presence).

Note: A user SHOULD NOT send a presence update to broadcast information that changes independently of the user's presence and availability for communication.

4.2.  Initial Presence

4.2.1.  Client Generation

After completing the preconditions described in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.) (REQUIRED) and requesting the roster (RECOMMENDED), a client SHOULD signal its availability for communication by sending INITIAL PRESENCE to its server, i.e., a presence stanza with no 'to' address (signalling that it is meant to be broadcasted by the server on behalf of the client) and no 'type' attribute (signalling the user's availability). After sending initial presence, a connected resource (in the terminology of [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.)) is said to be an AVAILABLE RESOURCE.

UC: <presence/>

4.2.2.  Server Processing of Outbound Presence

Upon receiving initial presence from a client, the user's server MUST send the initial presence stanza from the full JID <user@domain/resource> of the user to all contacts that are subscribed to the user's presence 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: In the following examples, the "user" is juliet@example.com and the user has three contacts in her roster with a subscription state of from or both: romeo@example.net, mercutio@example.com, and benvolio@example.com.

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

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

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

The user's server MUST also broadcast initial presence from the user's newly available resource to all of the user's available resources.

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

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

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

4.2.3.  Server Processing of Inbound Presence

Upon receiving presence from the user, the contact's server MUST deliver the user's presence stanza to the full JIDs <contact@domain/resource> associated with all of the contact's available resources.

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

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

4.2.4.  Client Processing of Inbound Presence

When the contact's client receives presence from the user and the user is in the contact's roster, it SHOULD display the presence information in an appropriate roster interface.

If the user is not in the contact's roster but the contact and the user are actively exchanging message or IQ stanzas, the contact's client SHOULD display the presence information in the user interface for that chat session.

Otherwise, the client SHOULD ignore the presence information and not display it to the contact.

4.3.  Presence Probes

A PRESENCE PROBE is a presence stanza whose 'type' attribute has a value of "probe". The value of the 'from' address SHOULD be the full JID <user@domain/resource> of the probing user and the value of the 'to' address SHOULD be the bare JID <contact@domain> of the contact whose availability the user wants to discover.

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

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

4.3.1.  Server Generation of Outbound Presence Probe

When a server needs to discover the availability of a user's contact, it SHOULD send a presence probe from the full JID <user@domain/resource> of the user to the bare JID <contact@domain> of the contact. The server SHOULD send a probe to a contact only if the contact is in the user's roster with the 'subscription' attribute set to a value of "to" or "both" (i.e., if the user is subscribed to the contact's presence).

The user's server SHOULD send a presence probe whenever the user starts a new presence session by sending initial presence; however, the server MAY choose not to send the probe at that point if it has what it deems to be reliable and up-to-date presence information about the user's contacts (e.g., because the user has another available resource or because the user briefly logged off and on before the new presence session began).

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

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

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

4.3.2.  Server Processing of Inbound Presence Probe

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

1. If the contact account does not exist or the user is in the contact's roster with a subscription state other than "From", "From + Pending Out", or "Both" (as defined under Appendix A (Subscription States)), the contact's server MUST return a presence stanza of type "unsubscribed" in response to the presence probe (however, if a server receives a presence probe from a configured hostname of the server itself or another such trusted service, it MAY provide presence information about the user to that entity).

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

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

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

4.4.  Subsequent Presence Broadcast

4.4.1.  Client Generation

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

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

4.4.2.  Server Processing of Outbound Presence

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

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

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

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

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

Note: As an optimization, if the subscription state is "both" then the user's server MAY choose to broadcast subsequent presence only if the server has received available presence from the contact at some point during the user's session; i.e., if the server never received available presence from the contact and the user has a mutual presence subscription with the contact, it MAY decline to send subsequent presence to the contact.

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

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

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

4.4.3.  Server Processing of Inbound Presence

Upon receiving presence from the user, the contact's server MUST deliver the user's presence stanza to the full JIDs <contact@domain/resource> associated with all of the contact's available resources.

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

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

4.4.4.  Client Processing of Inbound Presence

When the contact's client receives presence from the user and the user is in the contact's roster, it SHOULD display the presence information in an appropriate roster interface.

If the user is not in the contact's roster but the contact and the user are actively exchanging message or IQ stanzas, the contact's client SHOULD display the presence information in the user interface for that chat session.

Otherwise, the client SHOULD ignore the presence information and not display it to the contact.

4.5.  Unavailable Presence

4.5.1.  Client Generation

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

UC: <presence type='unavailable'/>

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

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

4.5.2.  Server Processing of Outbound Unavailable Presence

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

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

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

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

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

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

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

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

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

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

4.5.3.  Server Processing of Inbound Unavailable Presence

Upon receiving unavailable presence from the user, the contact's server MUST deliver the user's presence stanza to the full JIDs <contact@domain/resource> associated with all of the contact's available resources.

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

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

4.5.4.  Client Processing of Inbound Unavailable Presence

When the contact's client receives unavailable presence from the user and the user is in the contact's roster, it SHOULD display the unavailable presence information in an appropriate roster interface.

If the user is not in the contact's roster but the contact and the user are actively exchanging message or IQ stanzas, the contact's client SHOULD display the unavailable presence information in the user interface for that chat session.

Otherwise, the client SHOULD ignore the unavailable presence information and not display it to the contact.

4.6.  Directed Presence

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

4.6.1.  Client Generation

As noted, directed presence is a presence stanza with a 'to' attribute whose value is the bare JID or full JID of the other entity and with either no 'type' attribute or a 'type' attribute whose value is "unavailable".

4.6.2.  Server Processing of Outbound Directed Presence

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

1. If the user sends directed available or unavailable presence to a contact that is in the user's roster with a subscription type of "from" or "both" after having sent initial presence and before sending broadcasted unavailable presence, the user's server MUST route or deliver the full XML of that presence stanza but SHOULD NOT otherwise modify the contact's status regarding broadcasted presence (i.e., it SHOULD include the contact's JID in any subsequent presence broadcasts initiated by the user).
2. If the user sends directed presence to an entity that is not in the user's roster with a subscription type of "from" or "both" after having sent initial presence and before sending broadcasted unavailable presence, the user's server MUST route or deliver the full XML of that presence stanza to the entity but MUST NOT modify the contact's status regarding available presence broadcast (i.e., it MUST NOT include the entity's JID in any subsequent broadcasts of available presence initiated by the user); however, if the available resource from which the user sent the directed presence become unavailable, the user's server MUST route that unavailable presence to the entity (if the user has not yet sent directed unavailable presence to that entity).
3. If the user sends directed presence without first sending initial presence or after having sent unavailable presence broadcast (i.e., the resource is connected but not available), the user's server MUST treat the entities to which the user sends directed presence in the same way that it treats the entities listed in case #2 above.

4.6.3.  Server Processing of Inbound Directed Presence

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

4.6.4.  Client Processing of Inbound Directed Presence

When the contact's client receives presence from the user and the user is in the contact's roster, it SHOULD display the presence information in an appropriate roster interface.

If the user is not in the contact's roster but the contact and the user are actively exchanging message or IQ stanzas, the contact's client SHOULD display the presence information in an appropriate user interface.

Otherwise, the client SHOULD ignore the presence information and not display it to the contact.

4.7.  Presence Syntax

4.7.1.  Values of the Type Attribute

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

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

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

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

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

• error -- An error has occurred regarding processing of a previously-sent presence stanza; if the presence stanza is of type "error", it MUST include an <error/> child element (see see [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.)).
• probe -- A request for an entity's current presence; SHOULD be generated only by a server on behalf of a user.
• subscribe -- The sender wishes to subscribe to the recipient's presence.
• subscribed -- The sender has allowed the recipient to receive their presence.
• unsubscribe -- The sender is unsubscribing from another entity's presence.
• unsubscribed -- The subscription request has been denied or a previously-granted subscription has been cancelled.
• unavailable -- Signals that the entity is no longer available for communication.

4.7.2.  Child Elements

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

4.7.2.1.  Show

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

• away -- The entity or resource is temporarily away.
• chat -- The entity or resource is actively interested in chatting.
• dnd -- The entity or resource is busy (dnd = "Do Not Disturb").
• 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.

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

4.7.2.2.  Status

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

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

The <status/> element MUST NOT possess any attributes, with the exception of the 'xml:lang' attribute. Multiple instances of the <status/> element MAY be included, but only if each instance possesses an 'xml:lang' attribute with a distinct language value (either explicitly or by inheritance from the 'xml:lang' value of an element farther up in the XML hierarchy, which may include the XML stream header as described in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.)).

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

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

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

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

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

4.7.2.3.  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.

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

If no priority is provided, the processing server or client SHOULD consider the priority to be zero.

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

4.7.2.4.  Extended Content

As described in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.), an XML stanza MAY contain any properly-namespaced child element; this applies to the presence stanza as well.

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

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

5.  Exchanging Messages

Once a client has authenticated with a server and bound a resource to an XML stream as described in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.), an XMPP server will route XML stanzas to and from that client. One type of stanza that may be exchanged is <message/>. 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 Processing XML Stanzas (Server Rules for Processing XML Stanzas), the sender's server is responsible for delivering the message to the intended recipient (if the recipient is on the same server) or for routing the message to the recipient's server (if the recipient is on a different server). Thus a message stanza is used to "push" information to another entity.

5.1.  Attributes

5.1.1.  To Attribute

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

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

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

If the message is being sent in reply to a message previously received from an address of the form <user@domain/resource> (e.g., within the context of a 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.

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

5.1.2.  Type Attribute

Common uses of the message stanza in instant messaging applications include single messages, messages sent in the context of a chat conversation, messages sent in the context of a multi-user chat room, headlines and other alerts, and errors. These uses are differentiated via the 'type' attribute. Inclusion of the 'type' attribute is RECOMMENDED. If included, the 'type' attribute MUST have one of the following values:

• chat -- The message is sent in the context of a one-to-one chat conversation. A receiving client SHOULD present the message in an interface enabling one-to-one chat between the two parties, including an appropriate conversation history.
• error -- The message is generated by by an entity that experiences an error in processing a message received from another entity (for details regarding stanza error syntax, see [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.)). A client that receives a message of type "error" SHOULD present an appropriate interface informing the sender of the nature of the error.
• groupchat -- The message is sent in the context of a multi-user chat environment (similar to that of [IRC] (Kalt, C., “Internet Relay Chat: Architecture,” April 2000.)). A receiving client SHOULD present the message in an interface enabling many-to-many chat between the parties, including a roster of parties in the chatroom and an appropriate conversation history. Full definition of XMPP-based groupchat protocols is out of scope for this document (for details, see [XEP‑0045] (Saint-Andre, P., “Multi-User Chat,” April 2007.)).
• headline -- The message is probably generated by an automated service that delivers or broadcasts content (news, sports, market information, syndicated content, alerts, etc.) or the sender wishes the message to be delivered as if it were. No reply to the message is expected, and a receiving client SHOULD present the message in an interface that appropriately differentiates the message from standalone messages, chat sessions, or groupchat sessions (e.g., by not providing the recipient with the ability to reply). The receiving server SHOULD deliver the message to all of the recipient's available resources.
• 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 receiving client SHOULD present the message in an interface enabling the recipient to reply, but without a conversation history. This is the default value of the 'type' attribute.

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

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

5.2.  Child Elements

An XMPP message stanza MAY contain any allowable child elements qualified by the 'jabber:client' (or 'jabber:server') namespace, as well as any other properly-namespaced child element that consists of extended content. The defined payloads are described in the following sections and extended content payloads are described in the appropriate XMPP extension specifications (not herein).

5.2.1.  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.

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

The <body/> element MUST NOT possess any attributes, with the exception of the 'xml:lang' attribute. Multiple instances of the <body/> element MAY be included in a message stanza, but only if each instance possesses an 'xml:lang' attribute with a distinct language value (either explicitly or by inheritance from the 'xml:lang' value of an element farther up in the XML hierarchy, which may include the XML stream header as described in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.)).

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

The <body/> element MUST NOT contain mixed content (as defined in Section 3.2.2 of [XML] (Paoli, J., Maler, E., Sperberg-McQueen, C., Yergeau, F., and T. Bray, “Extensible Markup Language (XML) 1.0 (Fourth Edition),” August 2006.)).

5.2.2.  Subject

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

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

The <subject/> element MUST NOT possess any attributes, with the exception of the 'xml:lang' attribute. Multiple instances of the <subject/> element MAY be included for the purpose of providing alternate versions of the same subject, but only if each instance possesses an 'xml:lang' attribute with a distinct language value (either explicitly or by inheritance from the 'xml:lang' value of an element farther up in the XML hierarchy, which may include the XML stream header as described in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” July 2007.)).

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

The <subject/> element MUST NOT contain mixed content (as defined in Section 3.2.2 of [XML] (Paoli, J., Maler, E., Sperberg-McQueen, C., Yergeau, F., and T. Bray, “Extensible Markup Language (XML) 1.0 (Fourth Edition),” August 2006.)).

5.2.3.  Thread

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

The value of the <thread/> element MUST be a universally unique identifier (UUID) as described in [UUID] (Leach, P., Mealling, M., and R. Salz, “A Universally Unique IDentifier (UUID) URN Namespace,” July 2005.).

The use of the <thread/> element is OPTIONAL. The <thread/> element 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