相关词典网站：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).
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
Introduction . . . . . . . . . . . . . . . . . . . . . . . .
Syntax of XML Stanzas
. . . . . . . . . . . . . . . . . . .
Session Establishment
. . . . . . . . . . . . . . . . . . .
Exchanging Messages
. . . . . . . . . . . . . . . . . . . .
Exchanging Presence Information
. . . . . . . . . . . . . .
Managing Subscriptions . . . . . . . . . . . . . . . . . . .
Roster Management
. . . . . . . . . . . . . . . . . . . . .
Integration of Roster Items and Presence Subscriptions . . .
Subscription States
. . . . . . . . . . . . . . . . . . . .
Blocking Communication . . . . . . . . . . . . . . . . . . .
Server Rules for Handling XML Stanzas
. . . . . . . . . . .
IM and Presence Compliance Requirements
. . . . . . . . . .
Internationalization Considerations
. . . . . . . . . . . .
Security Considerations
. . . . . . . . . . . . . . . . . .
IANA Considerations
. . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . .
vCards . . . . . . . . . . . . . . . . . . . . . . . . . . .
XML Schemas. . . . . . . . . . . . . . . . . . . . . . . . .
Differences Between Jabber IM/Presence Protocols and XMPP. . 105
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . .
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . .
Author's Address. . . . . . . . . . . . . . . . . . . . . . . . . 106
Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 107
Introduction
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 , , and
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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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:
Exchange messages with other users
Exchange presence information with other users
Manage subscriptions to and from other users
Manage items in a contact list (in XMPP this is called a "roster")
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 instan i.e., it must be possible to use the
protocol to provide a presence service, an instant messaging service,
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].
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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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.
before addressing particular "use cases" for such applications, we
here further describe the syntax of XML stanzas, thereby
supplementing the discussion in [XMPP-CORE].
Message Syntax
Message stanzas qualified by the 'jabber:client' or 'jabber:server'
namespace are used to "push" information to another entity.
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.
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).
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 compliant client SHOULD present the message in an
interface enabling one-to-one chat between the two parties,
including an appropriate conversation history.
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.
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.
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).
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 for
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
Although the 'type' attribute is OPTIONAL, it is considered polite to
mirror the type in any
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').
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
If the message stanza is of type "error", it MUST include
for details, see [XMPP-CORE].
Otherwise, the
message stanza MAY contain any of the following child elements
without an explicit namespace declaration:
element contains human-readable XML character data
that specifies the topic of the message.
element MUST
NOT possess any attributes, with the exception of the 'xml:lang'
attribute.
Multiple instances of the
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.
element MUST NOT
contain mixed content (as defined in Section 3.2.2 of [XML]).
element contains human-readable XML character data that
specifies the textual con this child element is
normally included but is OPTIONAL.
element MUST NOT
possess any attributes, with the exception of the 'xml:lang'
attribute.
Multiple instances of the
element MAY be included
but only if each instance possesses an 'xml:lang' attribute with a
distinct language value.
element MUST NOT contain mixed
content (as defined in Section 3.2.2 of [XML]).
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
element is
generated by the sender and SHOULD be copied back in any replies.
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
element is OPTIONAL and is not used to identify individual
messages, only conversations.
A message stanza MUST NOT contain more
element MUST NOT possess
any attributes.
The value of the
element MUST be treated
a no semantic meaning may be derived from it,
and only exact comparisons may be made against it.
element MUST NOT contain mixed content (as defined in Section 3.2.2
of [XML]).
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
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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:
unavailable -- Signals that the entity is no longer available for
communication.
subscribe -- The sender wishes to subscribe to the recipient's
subscribed -- The sender has allowed the recipient to receive
their presence.
unsubscribe -- The sender is unsubscribing from another entity's
unsubscribed -- The subscription request has been denied or a
previously-granted subscription has been cancelled.
probe -- A request for an entity' SHOULD be
generated only by a server on behalf of a user.
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).
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
for details, see [XMPP-CORE].
presence stanza possesses no 'type' attribute, it MAY contain any of
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the following child elements (note that the
child MAY be
sent in a presence stanza of type "unavailable" or, for historical
reasons, "subscribe"):
The OPTIONAL
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
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):
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").
element is provided, the entity is assumed to be online
and available.
The OPTIONAL
element contains XML character data specifying
a natural-language description of availability status.
normally used in conjunction with the show element to provide a
detailed description of an availability state (e.g., "In a meeting").
element MUST NOT possess any attributes, with the
exception of the 'xml:lang' attribute.
Multiple instances of the
element MAY be included but only if each instance possesses
an 'xml:lang' attribute with a distinct language value.
The OPTIONAL
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
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).
IQ stanzas provide a structured request-response mechanism.
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 ).
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.
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
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 .
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.
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:
Stream Authentication -- a client MUST complete stream
authentication as documented in [XMPP-CORE] before attempting to
establish a session or send any XML stanzas.
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 , 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
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:
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
it completes this step by sending to the server an IQ
stanza of type "set" containing an empty
child element
qualified by the 'urn:ietf:params:xml:ns:xmpp-session' namespace:
Step 1: Client requests session with server:
Step 2: Server informs client that session has been created:
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):
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):
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
In case #1, the server SHOULD send a
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
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):
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Step 2 (alt): Server informs newly-requested session of resource
conflict (case #2):
After establishing a session, a client SHOULD send initial presence
and request its roster as described below, although these actions are
Note: Before allowing the creation of instant messaging and presence
sessions, a server MAY require prior account provisioning.
methods for account provisioning include account creation by a server
administrator as well as in-band account registration using the
'jabber:iq:register' the latter method is out of scope for
this memo, but is documented in [JEP-0077], published by the Jabber
Software Foundation [JSF].
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
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).
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
If the message is being
sent in reply to a message previously received from an address of the
(e.g., within the context of a chat
session), the value of the 'to' address SHOULD be of the form
rather than of the form
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
rather than of the form .
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:
Wherefore art thou, Romeo?
Specifying a Message Body
A message stanza MAY (and often will) contain a child
whose XML character data specifies the primary meaning of the message
(see Body (Section 2.1.2.2)).
Example: A message with a body:
Wherefore art thou, Romeo?
PročeŽ jsi ty, Romeo?
Specifying a Message Subject
A message stanza MAY contain one or more child
specifying the topic of the message (see Subject (Section 2.1.2.1)).
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Example: A message with a subject:
I implore you!
Úpěnlivě prosim!
Wherefore art thou, Romeo?
PročeŽ jsi ty, Romeo?
Specifying a Conversation Thread
A message stanza MAY contain a child
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:
Art thou not Romeo, and a Montague?
e0ffe42bb12b944a3a38
Neither, fair saint, if either thee dislike.
e0ffe42bb12b944a3a38
How cam'st thou hither, tell me, and wherefore?
e0ffe42bb12b944a3a38
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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.
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].
Client and Server Presence Responsibilities
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):
Send presence probes (i.e., presence stanzas whose 'type'
attribute is set to a value of "probe") from the full JID (e.g.,
) of the user to all contacts to which
the user is subscribed in order to determine if they are
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).)
Broadcast initial presence from the full JID (e.g.,
) of the user to all contacts that are
subscribed to the user's
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
() 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
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).
Presence Probes
Upon receiving a presence probe from the user, the contact's server
SHOULD reply as follows:
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
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
stanza error in response to the presence
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.
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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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
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:
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).
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
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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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
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
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.
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
rather than
, 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
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.
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.
Specifying Availability Status
A client MAY provide further information about its availability
status by using the
element (see Show (Section 2.2.2.1)).
Example: Availability status:
Specifying Detailed Status Information
In conjunction with the
element, a client MAY provide
detailed status information by using the
element (see
Status (Section 2.2.2.2)).
Example: Detailed status information:
Wooing Juliet
Ja dvořím Juliet
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Specifying Presence Priority
A client MAY provide a priority for its resource by using the
element (see Priority (Section 2.2.2.3)).
Example: Presence priority:
Wooing Juliet
Ja dvořím Juliet
Presence Examples
The examples in this section illustrate the presence-related
protocols described above.
The user is , he has an
available resource whose resource identifier is "orchard", and he has
the following individuals in his roster:
(subscription="both" and she has two available
resources, one whose resource is "chamber" and another whose
resource is "balcony")
benvolio@example.org (subscription="to")
mercutio@example.org (subscription="from")
Example 1: User sends initial 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:
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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:
Example 4: Contacts' servers reply to presence probe on behalf of all
available resources:
be right back
gallivanting
Example 5: Contacts' servers deliver user's initial presence to all
available resources or return error to user:
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Example 6: User sends directed presence to another user not in his
courting Juliet
Example 7: User sends updated available presence information for
broadcasting:
I shall return!
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):
I shall return!
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Example 9: Contact's server delivers updated presence information to
all of the contact's available resources:
[to "balcony" resource...]
I shall return!
[to "chamber" resource...]
I shall return!
Example 10: One of the contact's resources broadcasts final presence:
Example 11: Contact's server sends unavailable presence information
Example 12: User sends final 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
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.
subscription l 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
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.
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:
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For client and server responsibilities regarding presence
subscription requests, refer to Presence Subscriptions (Section
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:
Example: Refusing a presence subscription request:
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:
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:
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 ).
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
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.
Syntax and Semantics
Rosters are managed using IQ stanzas, specifically by means of a
child element qualified by the 'jabber:iq:roster' namespace.
element MAY contain one or more
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
element (which is
REQUIRED).
The value of the 'jid' attribute SHOULD be of the form
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
Allowable 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
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.
element MAY contain one or more
child elements,
for use in collecting roster items into various categories.
character data of the
element is opaque.
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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
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
) or full JID (of the form );
otherwise, the client SHOULD ignore the "roster push".
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:
Example: Client receives roster from server:
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Adding a Roster Item
At any time, a user MAY add an item to his or her roster.
Example: Client adds a new item:
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:
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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:
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):
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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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
Example: Client removes an item:
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
Integration of Roster Items and Presence Subscriptions
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.
section describes the level of integration that MUST be supported
within XMPP instant messaging applications.
There are four primary subscription states:
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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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 (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 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]).
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.
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
element qualified by
the 'jabber:iq:roster' namespace, which in turn contains an
element that defines the
element MUST possess a 'jid' attribute, MAY possess a 'name'
attribute, MUST NOT possess a 'subscription' attribute, and MAY
contain one or more
child elements:
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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:
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:
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' this pending sub-state is denoted by
the inclusion of the ask='subscribe' attribute in the roster
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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
child shown above.
The user's server MUST also stamp the presence stanza of type
"subscribe" with the user's bare JID (i.e., )
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
however, if the contact is served by the same
host, then the server can simply deliver the presence stanza
directly):
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.
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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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
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
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
succe (3) MUST route the presence stanza of
type "subscribed" to the user, first stamping the 'from' address
as the bare JID () and (4)
MUST send available presence from all of the contact's available
resources to the user:
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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
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 (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:
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"
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
from the perspective of the
contact, there now exists a subscription from the user.
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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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):
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 () of the contact:
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.
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:
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"
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.
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.
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):
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
and (2) MUST route the presence stanza of type "subscribe"
to the user, first stamping the 'from' address as the bare JID
() of the contact:
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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.
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
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
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 ()
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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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.
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
(2) MUST initiate a roster push to all available
resources associated with the contact that have requested the
roster, containing an updated roster item for the user with the
'subscription' attribute set to a value of "both"; and (3) MUST
deliver the available presence stanza received from each of the
user's available resources to each of the contact's available
resources:
Saint-Andre
Standards Track
October 2004
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" 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".
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.
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):
Saint-Andre
Standards Track
October 2004
As a result, the user's server MUST route the presence stanza of
t