XMPP Working Group P. Saint-Andre (ed.)
Internet-Draft Jabber Software Foundation
Expires: July 6, 2004 January 6, 2004
Extensible Messaging and Presence Protocol (XMPP): Core
draft-ietf-xmpp-core-21
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This memo defines the core features of the Extensible Messaging and
Presence Protocol (XMPP), a protocol for streaming Extensible Markup
Language (XML) elements in order to exchange structured information
in close to real time between any two network endpoints. While XMPP
provides a generalized, extensible framework for exchanging XML data,
it is used mainly for the purpose of building instant messaging and
presence applications that meet the requirements of RFC 2779.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Generalized Architecture . . . . . . . . . . . . . . . . . . . 4
3. Addressing Scheme . . . . . . . . . . . . . . . . . . . . . . 6
4. XML Streams . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Use of TLS . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6. Use of SASL . . . . . . . . . . . . . . . . . . . . . . . . . 26
7. Resource Binding . . . . . . . . . . . . . . . . . . . . . . . 36
8. Server Dialback . . . . . . . . . . . . . . . . . . . . . . . 39
9. XML Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 46
10. Server Rules for Handling XML Stanzas . . . . . . . . . . . . 55
11. XML Usage within XMPP . . . . . . . . . . . . . . . . . . . . 57
12. Core Compliance Requirements . . . . . . . . . . . . . . . . . 60
13. Internationalization Considerations . . . . . . . . . . . . . 61
14. Security Considerations . . . . . . . . . . . . . . . . . . . 61
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 66
Normative References . . . . . . . . . . . . . . . . . . . . . 69
Informative References . . . . . . . . . . . . . . . . . . . . 71
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 72
A. Nodeprep . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
B. Resourceprep . . . . . . . . . . . . . . . . . . . . . . . . . 74
C. XML Schemas . . . . . . . . . . . . . . . . . . . . . . . . . 76
D. Differences Between Core Jabber Protocol and XMPP . . . . . . 83
E. Revision History . . . . . . . . . . . . . . . . . . . . . . . 85
Intellectual Property and Copyright Statements . . . . . . . . 94
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1. Introduction
1.1 Overview
The Extensible Messaging and Presence Protocol (XMPP) is an open XML
[XML] protocol for near-real-time messaging, presence, and
request-response services. The basic syntax and semantics were
developed originally within the Jabber open-source community, mainly
in 1999. In 2002, the XMPP WG was chartered with developing an
adaptation of the Jabber protocol that would be suitable as an IETF
instant messaging (IM) and presence technology. As a result of work
by the XMPP WG, the current memo defines the core features of XMPP;
Extensible Messaging and Presence Protocol (XMPP): Instant Messaging
and Presence [XMPP-IM] defines the extensions required to provide the
instant messaging and presence functionality defined in RFC 2779
[IMP-REQS].
1.2 Terminology
The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [TERMS].
1.3 Contributors
Most of the core aspects of the Extensible Messaging and Presence
Protocol were developed originally within the Jabber open-source
community in 1999. This community was founded by Jeremie Miller, who
released source code for the initial version of the jabberd server in
January 1999. Major early contributors to the base protocol also
included Ryan Eatmon, Peter Millard, Thomas Muldowney, and Dave
Smith. Work by the XMPP Working Group has concentrated especially on
security and internationalization; in these areas, protocols for the
use of TLS and SASL were originally contributed by Rob Norris, and
stringprep profiles were originally contributed by Joe Hildebrand.
The error code syntax was suggested by Lisa Dusseault.
1.4 Acknowledgements
Thanks are due to a number of individuals in addition to the
contributors listed. Although it is difficult to provide a complete
list, the following individuals were particularly helpful in defining
the protocols or in commenting on the specifications in this memo:
Thomas Charron, Richard Dobson, Sam Hartman, Schuyler Heath, Jonathan
Hogg, Craig Kaes, Jacek Konieczny, Alexey Melnikov, Keith Minkler,
Julian Missig, Pete Resnick, Marshall Rose, Alexey Shchepin,
Jean-Louis Seguineau, Iain Shigeoka, and David Waite. Thanks also to
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members of the XMPP Working Group and the IETF community for comments
and feedback provided throughout the life of this memo.
2. Generalized Architecture
2.1 Overview
Although XMPP is not wedded to any specific network architecture, to
date it usually has been implemented via a typical client-server
architecture, wherein a client utilizing XMPP accesses a server over
a TCP [TCP] socket.
The following diagram provides a high-level overview of this
architecture (where "-" represents communications that use XMPP and
"=" represents communications that use any other protocol).
C1 - S1 - S2 - C3
/ \
C2 - G1 = FN1 = FC1
The symbols are as follows:
o C1, C2, C3 -- XMPP clients
o S1, S2 -- XMPP servers
o G1 -- A gateway that translates between XMPP and the protocol(s)
used on a foreign (non-XMPP) messaging network
o FN1 -- A foreign messaging network
o FC1 -- A client on a foreign messaging network
2.2 Server
A server acts as an intelligent abstraction layer for XMPP
communications. Its primary responsibilities are:
o to manage connections from or sessions for other entities, in the
form of XML streams (Section 4) to and from authorized clients,
servers, and other entities
o to route appropriately-addressed XML stanzas (Section 9) among
such entities over XML streams
Most XMPP-compliant servers also assume responsibility for the
storage of data that is used by clients (e.g., contact lists for
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users of XMPP-based instant messaging and presence applications); in
this case, the XML data is processed directly by the server itself on
behalf of the client and is not routed to another entity.
2.3 Client
Most clients connect directly to a server over a [TCP] socket and use
XMPP to take full advantage of the functionality provided by a server
and any associated services. Although there is no necessary coupling
of an XML stream to a TCP socket (e.g., a client could connect via
HTTP [HTTP] polling or some other mechanism), this specification
defines a binding of XMPP to TCP only. Multiple resources (e.g.,
devices or locations) MAY connect simultaneously to a server on
behalf of each authorized client, with each resource differentiated
by the resource identifier of an XMPP address (e.g., <node@domain/
home> vs. <node@domain/work>) as defined under Addressing Scheme
(Section 3). The RECOMMENDED port for connections between a client
and a server is 5222, as registered with the IANA (see Port Numbers
(Section 15.9)).
2.4 Gateway
A gateway is a special-purpose server-side service whose primary
function is to translate XMPP into the protocol used by a foreign
(non-XMPP) messaging system, as well as to translate the return data
back into XMPP. Examples are gateways to Internet Relay Chat (IRC),
Short Message Service (SMS), SIMPLE, SMTP, and legacy instant
messaging networks such as AIM, ICQ, MSN Messenger, and Yahoo!
Instant Messenger. Communications between gateways and servers, and
between gateways and the foreign messaging system, are not defined in
this document.
2.5 Network
Because each server is identified by a network address and because
server-to-server communications are a straightforward extension of
the client-to-server protocol, in practice the system consists of a
network of servers that inter-communicate. Thus user-a@domain1 is
able to exchange messages, presence, and other information with
user-b@domain2. This pattern is familiar from messaging protocols
(such as SMTP) that make use of network addressing standards.
Communications between any two servers are OPTIONAL. If enabled,
such communications SHOULD occur over XML streams that are bound to
[TCP] sockets. The RECOMMENDED port for connections between servers
is 5269, as registered with the IANA (see Port Numbers (Section
15.9)).
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3. Addressing Scheme
3.1 Overview
An entity is anything that can be considered a network endpoint
(i.e., an ID on the network) and that can communicate using XMPP.
All such entities are uniquely addressable in a form that is
consistent with RFC 2396 [URI]. For historical reasons, the address
of an XMPP entity is called a Jabber Identifier or JID. A valid JID
contains a set of ordered elements formed of a domain identifier,
node identifier, and resource identifier.
The syntax for a JID is defined below using Augmented Backus-Naur
Form as defined in [ABNF]. The IPv4address and IPv6address rules are
defined in Appendix B of [IPv6]; the allowable character sequences
that conform to the node rule are defined by the Nodeprep (Appendix
A) profile of [STRINGPREP] as documented in this memo; the allowable
character sequences that conform to the resource rule are defined by
the Resourceprep (Appendix B) profile of [STRINGPREP] as documented
in this memo; and the sub-domain rule makes reference to the concept
of a domain label as described in [IDNA].
jid = [ node "@" ] domain [ "/" resource ]
domain = fqdn / address-literal
fqdn = (sub-domain 1*("." sub-domain))
sub-domain = ([IDNA] conformant domain label)
address-literal = IPv4address / IPv6address
All JIDs are based on the foregoing structure. The most common use
of this structure is to identify an instant messaging user, the
server to which the user connects, and the user's connected resource
(e.g., a specific client) in the form of <user@host/resource>.
However, node types other than clients are possible; for example, a
specific chat room offered by a multi-user chat service could be
addressed as <room@service> (where "room" is the name of the chat
room and "service" is the hostname of the multi-user chat service)
and a specific occupant of such a room could be addressed as
<room@service/nick> (where "nick" is the occupant's room nickname).
Many other JID types are possible (e.g., <domain/resource> could be a
server-side script or service).
Each allowable portion of a JID (node identifier, domain identifier,
and resource identifier) MUST NOT be more than 1023 bytes in length,
resulting in a maximum total size (including the '@' and '/'
separators) of 3071 bytes.
3.2 Domain Identifier
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The domain identifier is the primary identifier and is the only
REQUIRED element of a JID (a mere domain identifier is a valid JID).
It usually represents the network gateway or "primary" server to
which other entities connect for XML routing and data management
capabilities. However, the entity referenced by a domain identifier
is not always a server, and may be a service that is addressed as a
subdomain of a server and that provides functionality above and
beyond the capabilities of a server (e.g., a multi-user chat service,
a user directory, or a gateway to a foreign messaging system).
The domain identifier for every server or service that will
communicate over a network MAY be an IP address but SHOULD be a fully
qualified domain name (see [DNS]). A domain identifier MUST be an
"internationalized domain name" as defined in [IDNA], to which the
Nameprep [NAMEPREP] profile of stringprep [STRINGPREP] can be applied
without failing. Before comparing two domain identifiers, a server
MUST (and a client SHOULD) first apply the Nameprep profile to the
labels (as defined in [IDNA]) that make up each identifier.
3.3 Node Identifier
The node identifier is an optional secondary identifier placed before
the domain identifier and separated from the latter by the '@'
character. It usually represents the entity requesting and using
network access provided by the server or gateway (i.e., a client),
although it can also represent other kinds of entities (e.g., a chat
room associated with a multi-user chat service). The entity
represented by a node identifier is addressed within the context of a
specific domain; within instant messaging and presence applications
of XMPP this address is called a "bare JID" and is of the form
<node@domain>.
A node identifier MUST be formatted such that the Nodeprep (Appendix
A) profile of [STRINGPREP] can be applied to it without failing.
Before comparing two node identifiers, a server MUST (and a client
SHOULD) first apply the Nodeprep profile to each identifier.
3.4 Resource Identifier
The resource identifier is an optional tertiary identifier placed
after the domain identifier and separated from the latter by the '/'
character. A resource identifier may modify either a <node@domain>
or mere <domain> address. It usually represents a specific session,
connection (e.g., a device or location), or object (e.g., a
participant in a multi-user chat room) belonging to the entity
associated with a node identifier. A resource identifier is opaque
to both servers and other clients, and is typically defined by a
client implementation when it provides the information necessary to
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complete Resource Binding (Section 7) (although it may be generated
by a server on behalf of a client), after which it is referred to as
a "connected resource". An entity MAY maintain multiple connected
resources simultaneously, with each connected resource differentiated
by a distinct resource identifier.
A resource identifier MUST be formatted such that the Resourceprep
(Appendix B) profile of [STRINGPREP] can be applied to it without
failing. Before comparing two resource identifiers, a server MUST
(and a client SHOULD) first apply the Resourceprep profile to each
identifier.
3.5 Determination of Addresses
After SASL negotiation (Section 6) and, if appropriate, Resource
Binding (Section 7), the receiving entity for a stream MUST determine
the initiating entity's JID.
For server-to-server communications, the initiating entity's JID
SHOULD be the authorization identity, derived from the authentication
identity as defined by the Simple Authentication and Security Layer
(SASL) specification [SASL] if no authorization identity was
specified during SASL negotiation (Section 6).
For client-to-server communications, the "bare JID" (<node@domain>)
SHOULD be the authorization identity, derived from the authentication
identity as defined in [SASL] if no authorization identity was
specified during SASL negotiation (Section 6); the resource
identifier portion of the "full JID" (<node@domain/resource>) SHOULD
be the resource identifier negotiated by the client and server during
Resource Binding (Section 7).
The receiving entity MUST ensure that the resulting JID (including
node identifier, domain identifier, resource identifier, and
separator characters) conforms to the rules and formats defined
earlier in this section; to meet this restriction, the receiving
entity may need to replace the JID sent by the initiating entity with
the canonicalized JID as determined by the receiving entity.
4. XML Streams
4.1 Overview
Two fundamental concepts make possible the rapid, asynchronous
exchange of relatively small payloads of structured information
between presence-aware entities: XML streams and XML stanzas. These
terms are defined as follows:
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Definition of XML Stream: An XML stream is a container for the
exchange of XML elements between any two entities over a network.
An XML stream is negotiated from an initiating entity (usually a
client or server) to a receiving entity (usually a server),
normally over a [TCP] socket, and corresponds to the initiating
entity's "session" with the receiving entity. The start of the
XML stream is denoted unambiguously by an opening XML <stream> tag
(with appropriate attributes and namespace declarations), while
the end of the XML stream is denoted unambiguously by a closing
XML </stream> tag. An XML stream is unidirectional; in order to
enable bidirectional information exchange, the initiating entity
and receiving entity MUST negotiate one stream in each direction
(the "initial stream" and the "response stream"), normally over
the same TCP connection.
Definition of XML Stanza: An XML stanza is a discrete semantic unit
of structured information that is sent from one entity to another
over an XML stream. An XML stanza exists at the direct child
level of the root <stream/> element and is said to be
well-balanced if it matches production [43] content of [XML]. The
start of any XML stanza is denoted unambiguously by the element
start tag at depth=1 of the XML stream (e.g., <presence>), and the
end of any XML stanza is denoted unambiguously by the
corresponding close tag at depth=1 (e.g., </presence>). An XML
stanza MAY contain child elements (with accompanying attributes,
elements, and CDATA) as necessary in order to convey the desired
information. The only defined XML stanzas are <message/>,
<presence/>, and <iq/> as defined under XML Stanzas (Section 9);
an XML element sent for the purpose of Transport Layer Security
(TLS) negotiation (Section 5), Simple Authentication and Security
Layer (SASL) negotiation (Section 6), or server dialback (Section
8) is not considered to be an XML stanza.
Consider the example of a client's session with a server. In order
to connect to a server, a client MUST initiate an XML stream by
sending an opening <stream> tag to the server, optionally preceded by
a text declaration specifying the XML version and the character
encoding supported (see Inclusion of Text Declaration (Section 11.4);
see also Character Encoding (Section 11.5)). Subject to local
policies and service provisioning, the server SHOULD then reply with
a second XML stream back to the client, again optionally preceded by
a text declaration. Once the client has completed SASL negotiation
(Section 6), the client MAY send an unbounded number of XML stanzas
over the stream to any recipient on the network. When the client
desires to close the stream, it simply sends a closing </stream> tag
to the server (alternatively, the stream may be closed by the
server), after which both the client and server SHOULD close the
underlying TCP connection as well.
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Those who are accustomed to thinking of XML in a document-centric
manner may wish to view a client's session with a server as
consisting of two open-ended XML documents: one from the client to
the server and one from the server to the client. From this
perspective, the root <stream/> element can be considered the
document entity for each "document", and the two "documents" are
built up through the accumulation of XML stanzas sent over the two
XML streams. However, this perspective is a convenience only, and
XMPP does not deal in documents but in XML streams and XML stanzas.
In essence, then, an XML stream acts as an envelope for all the XML
stanzas sent during a session. We can represent this in a simplistic
fashion as follows:
|--------------------|
| <stream> |
|--------------------|
| <presence> |
| <show/> |
| </presence> |
|--------------------|
| <message to='foo'> |
| <body/> |
| </message> |
|--------------------|
| <iq to='bar'> |
| <query/> |
| </iq> |
|--------------------|
| ... |
|--------------------|
| </stream> |
|--------------------|
4.2 Stream Attributes
The attributes of the stream element are as follows:
o to -- The 'to' attribute SHOULD be used only in the XML stream
header from the initiating entity to the receiving entity, and
MUST be set to a hostname serviced by the receiving entity. There
SHOULD be no 'to' attribute set in the XML stream header by which
the receiving entity replies to the initiating entity; however, if
a 'to' attribute is included, it SHOULD be silently ignored by the
initiating entity.
o from -- The 'from' attribute SHOULD be used only in the XML stream
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header from the receiving entity to the initiating entity, and
MUST be set to a hostname serviced by the receiving entity that is
granting access to the initiating entity. There SHOULD be no
'from' attribute on the XML stream header sent from the initiating
entity to the receiving entity; however, if a 'from' attribute is
included, it SHOULD be silently ignored by the receiving entity.
o id -- The 'id' attribute SHOULD be used only in the XML stream
header from the receiving entity to the initiating entity. This
attribute is a unique identifier created by the receiving entity
to function as a session key for the initiating entity's streams
with the receiving entity, and MUST be unique within the receiving
application (normally a server). Note well that the stream ID may
be security-critical and therefore MUST be both unpredictable and
non-repeating. There SHOULD be no 'id' attribute on the XML
stream header sent from the initiating entity to the receiving
entity; however, if an 'id' attribute is included, it SHOULD be
silently ignored by the receiving entity.
o xml:lang -- An 'xml:lang' attribute (as defined in Section 2.12 of
[XML]) SHOULD be included by the initiating entity on the header
for the initial stream to specify the default language of any
human-readable XML character data it sends over that stream. If
the attribute is included, the receiving entity SHOULD remember
that value as the default for both the initial stream and the
response stream; if the attribute is not included, the receiving
entity SHOULD use a configurable default value for both streams,
which it MUST communicate in the header for the response stream.
For all stanzas sent over the initial stream, if the initiating
entity does not include an 'xml:lang' attribute, the receiving
entity SHOULD apply the default value; if the initiating entity
does include an 'xml:lang' attribute, the receiving entity MUST
NOT modify or delete it (see also xml:lang (Section 9.1.5)). The
value of the 'xml:lang' attribute MUST be an NMTOKEN (as defined
in Section 2.3 of [XML]) and MUST conform to the format defined in
RFC 3066 [LANGTAGS].
o version -- The presence of the version attribute set to a value of
"1.0" signals support for the stream-related protocols (including
stream features) defined in this specification. Detailed rules
regarding generation and handling of this attribute are defined
below.
We can summarize as follows:
| initiating to receiving | receiving to initiating
---------+---------------------------+-----------------------
to | hostname of receiver | silently ignored
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from | silently ignored | hostname of receiver
id | silently ignored | session key
xml:lang | default language | default language
version | signals XMPP 1.0 support | signals XMPP 1.0 support
4.2.1 Version Support
The version of XMPP specified herein is "1.0"; in particular, this
encapsulates the stream-related protocols (Use of TLS (Section 5),
Use of SASL (Section 6), and Stream Errors (Section 4.6)) as well as
the semantics of the three defined XML stanza types (<message/>,
<presence/>, and <iq/>). The major version number should be
incremented only if the stream and stanza formats or required actions
have changed so dramatically that an older version entity would not
be able to interoperate with a newer version entity if it simply
ignored the elements and attributes it did not understand and took
the actions specified in the older specification. The minor version
number indicates new capabilities, and MUST be ignored by an entity
with a smaller minor version number, but used for informational
purposes by the node with the larger minor version number. For
example, a minor version number might indicate the ability to process
a newly defined value of the 'type' attribute for message, presence,
or IQ stanzas; the node with the larger minor version number would
simply note that its correspondent would not be able to understand
that value of the 'type' attribute and therefore would not send it.
The following rules apply to the generation and handling by
implementations of the 'version' attribute within stream headers:
1. The initiating entity MUST set the value of the 'version'
attribute on the initial stream header to the highest version
number it supports (e.g., if the highest version number it
supports is that defined in this specification, it MUST set the
value to "1.0").
2. The receiving entity MUST set the value of the 'version'
attribute on the response stream header to either the value
supplied by the initiating entity or highest version number
supported by the receiving entity, whichever is lower. The
receiving entity MUST perform a numeric comparison, not a string
match.
3. If the version number included in the response stream header is
at least one major version lower than the version number included
in the initial stream header and newer version entities cannot
interoperate with older version entities as described above, the
initiating entity SHOULD generate an <unsupported-version/>
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stream error and terminate the XML stream and underlying TCP
connection.
4. If either entity receives a stream header with no 'version'
attribute, the entity MUST consider the version supported by the
other entity to be "0.0" and SHOULD NOT include a 'version'
attribute in the stream header it sends in reply.
4.3 Namespace Declarations
The stream element MUST possess both a streams namespace declaration
and a default namespace declaration (as "namespace declaration" is
defined in the XML namespaces specification [XML-NAMES]). For
detailed information regarding the streams namespace and default
namespace, see Namespace Names and Prefixes (Section 11.2).
4.4 Stream Features
If the initiating entity includes the 'version' attribute set to a
value of "1.0" in the initial stream header, the receiving entity
MUST send a <features/> child element (prefixed by the streams
namespace prefix) to the initiating entity in order to announce any
stream-level features that can be negotiated (or capabilities that
otherwise need to be advertised). Currently this is used only to
advertise Use of TLS (Section 5), Use of SASL (Section 6), and
Resource Binding (Section 7) as defined herein, and for Session
Establishment as defined in [XMPP-IM]; however, the stream features
functionality could be used to advertise other negotiable features in
the future. If an entity does not understand or support some
features, it SHOULD silently ignore them.
4.5 Stream Security
When negotiating XML streams in XMPP 1.0, TLS SHOULD be used as
defined under Use of TLS (Section 5) and SASL MUST be used as defined
under Use of SASL (Section 6). If the initiating entity attempts to
send an XML Stanza (Section 9) before the stream has been
authenticated, the receiving entity SHOULD return a <not-authorized/>
stream error to the initiating entity and then terminate both the XML
stream and the underlying TCP connection.
4.6 Stream Errors
The root stream element MAY contain an <error/> child element that is
prefixed by the streams namespace prefix. The error child MUST be
sent by a compliant entity (usually a server rather than a client) if
it perceives that a stream-level error has occurred.
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4.6.1 Rules
The following rules apply to stream-level errors:
o It is assumed that all stream-level errors are unrecoverable;
therefore, if an error occurs at the level of the stream, the
entity that detects the error MUST send a stream error to the
other entity, send a closing </stream> tag, and terminate the
underlying TCP connection.
o If the error occurs while the stream is being set up, the
receiving entity MUST still send the opening <stream> tag, include
the <error/> element as a child of the stream element, send the
closing </stream> tag, and terminate the underlying TCP
connection. In this case, if the initiating entity provides an
unknown host in the 'to' attribute (or provides no 'to' attribute
at all), the server SHOULD provide the server's authoritative
hostname in the 'from' attribute of the stream header sent before
termination.
4.6.2 Syntax
The syntax for stream errors is as follows:
<stream:error>
<defined-condition xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
<text xmlns='urn:ietf:params:xml:ns:xmpp-streams'>
OPTIONAL descriptive text
</text>
[OPTIONAL application-specific condition element]
</stream:error>
The <error/> element:
o MUST contain a child element corresponding to one of the defined
stanza error conditions defined below; this element MUST be
qualified by the 'urn:ietf:params:xml:ns:xmpp-streams' namespace
o MAY contain a <text/> child containing CDATA that describes the
error in more detail; this element MUST be qualified by the
'urn:ietf:params:xml:ns:xmpp-streams' namespace and SHOULD possess
an 'xml:lang' attribute
o MAY contain a child element for an application-specific error
condition; this element MUST be qualified by an
application-defined namespace, and its structure is defined by
that namespace
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The <text/> element is OPTIONAL. If included, it SHOULD be used only
to provide descriptive or diagnostic information that supplements the
meaning of a defined condition or application-specific condition. It
SHOULD NOT be interpreted programmatically by an application. It
SHOULD NOT be used as the error message presented to a user, but MAY
be shown in addition to the error message associated with the
included condition element (or elements).
4.6.3 Defined Conditions
The following stream-level error conditions are defined:
o <bad-format/> -- the entity has sent XML that cannot be processed;
this error MAY be used rather than more specific XML-related
errors such as <bad-namespace-prefix/>, <invalid-xml/>,
<restricted-xml/>, <unsupported-encoding/>, and
<xml-not-well-formed/>, although the more specific errors are
preferred.
o <bad-namespace-prefix/> -- the entity has sent a namespace prefix
that is unsupported, or has sent no namespace prefix on an element
that requires such a prefix (see XML Namespace Names and Prefixes
(Section 11.2)).
o <conflict/> -- the server is closing the active stream for this
entity because a new stream has been initiated that conflicts with
the existing stream.
o <connection-timeout/> -- the entity has not generated any traffic
over the stream for some period of time (configurable according to
a local service policy).
o <host-gone/> -- the value of the 'to' attribute provided by the
initiating entity in the stream header corresponds to a hostname
that is no longer hosted by the server.
o <host-unknown/> -- the value of the 'to' attribute provided by the
initiating entity in the stream header does not correspond to a
hostname that is hosted by the server.
o <improper-addressing/> -- a stanza sent between two servers lacks
a 'to' or 'from' attribute (or the attribute has no value).
o <internal-server-error/> -- the server has experienced a
misconfiguration or an otherwise-undefined internal error that
prevents it from servicing the stream.
o <invalid-from/> -- the JID or hostname provided in a 'from'
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address does not match an authorized JID or validated domain
negotiated between servers via SASL or dialback, or between a
client and a server via authentication and resource binding.
o <invalid-id/> -- the stream ID or dialback ID is invalid or does
not match an ID previously provided.
o <invalid-namespace/> -- the streams namespace name is something
other than "http://etherx.jabber.org/streams" or the dialback
namespace name is something other than "jabber:server:dialback"
(see XML Namespace Names and Prefixes (Section 11.2)).
o <invalid-xml/> -- the entity has sent invalid XML over the stream
to a server that performs validation (see Validation (Section
11.3)).
o <not-authorized/> -- the entity has attempted to send data before
the stream has been authenticated, or otherwise is not authorized
to perform an action related to stream negotiation; the receiving
entity MUST NOT process the offending stanza before sending the
stream error.
o <policy-violation/> -- the entity has violated some local service
policy; the server MAY choose to specify the policy in the <text/>
element.
o <remote-connection-failed/> -- the server is unable to properly
connect to a remote entity that is required for authentication or
authorization.
o <resource-constraint/> -- the server lacks the system resources
necessary to service the stream.
o <restricted-xml/> -- the entity has attempted to send restricted
XML features such as a comment, processing instruction, DTD,
entity reference, or unescaped character (see Restrictions
(Section 11.1)).
o <see-other-host/> -- the server will not provide service to the
initiating entity but is redirecting traffic to another host; the
server SHOULD specify the alternate hostname or IP address (which
MUST be a valid domain identifier) in the CDATA of the
<see-other-host/> element.
o <system-shutdown/> -- the server is being shut down and all active
streams are being closed.
o <undefined-condition/> -- the error condition is not one of those
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defined by the other conditions in this list; this error condition
SHOULD be used only in conjunction with an application-specific
condition.
o <unsupported-encoding/> -- the initiating entity has encoded the
stream in an encoding that is not supported by the server (see
Character Encoding (Section 11.5)).
o <unsupported-stanza-type/> -- the initiating entity has sent a
first-level child of the stream that is not supported by the
server.
o <unsupported-version/> -- the value of the 'version' attribute
provided by the initiating entity in the stream header specifies a
version of XMPP that is not supported by the server; the server
MAY specify the version(s) it supports in the <text/> element.
o <xml-not-well-formed/> -- the initiating entity has sent XML that
is not well-formed as defined by [XML].
4.6.4 Application-Specific Conditions
As noted, an application MAY provide application-specific stream
error information by including a properly-namespaced child in the
error element. The application-specific element SHOULD supplement or
further qualify a defined element. Thus the <error/> element will
contain two or three child elements:
<stream:error>
<xml-not-well-formed
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
<text xml:lang='en' xmlns='urn:ietf:params:xml:ns:xmpp-streams'>
Some special application diagnostic information!
</text>
<escape-your-data xmlns='application-ns'/>
</stream:error>
</stream:stream>
4.7 Simplified Stream Examples
This section contains two simplified examples of a stream-based
"session" of a client on a server (where the "C" lines are sent from
the client to the server, and the "S" lines are sent from the server
to the client); these examples are included for the purpose of
illustrating the concepts introduced thus far.
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A basic "session":
C: <?xml version='1.0'?>
<stream:stream
to='example.com'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='someid'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
... encryption, authentication, and resource binding ...
C: <message from='juliet@example.com'
to='romeo@example.net'
xml:lang='en'>
C: <body>Art thou not Romeo, and a Montague?</body>
C: </message>
S: <message from='romeo@example.net'
to='juliet@example.com'
xml:lang='en'>
S: <body>Neither, fair saint, if either thee dislike.</body>
S: </message>
C: </stream:stream>
S: </stream:stream>
A "session" gone bad:
C: <?xml version='1.0'?>
<stream:stream
to='example.com'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='someid'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
... encryption, authentication, and resource binding ...
C: <message xml:lang='en'>
<body>Bad XML, no closing body tag!
</message>
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S: <stream:error>
<xml-not-well-formed
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
S: </stream:stream>
5. Use of TLS
5.1 Overview
XMPP includes a method for securing the stream from tampering and
eavesdropping. This channel encryption method makes use of the
Transport Layer Security (TLS) protocol [TLS], along with a
"STARTTLS" extension that is modelled after similar extensions for
the IMAP [IMAP], POP3 [POP3], and ACAP [ACAP] protocols as described
in RFC 2595 [USINGTLS]. The namespace name for the STARTTLS
extension is 'urn:ietf:params:xml:ns:xmpp-tls'.
An administrator of a given domain MAY require the use of TLS for
client-to-server communications, server-to-server communications, or
both. Clients SHOULD use TLS to secure the streams prior to
attempting to complete SASL negotiation (Section 6), and servers
SHOULD use TLS between two domains for the purpose of securing
server-to-server communications.
The following rules apply:
1. An initiating entity that complies with this specification MUST
include the 'version' attribute set to a value of "1.0" in the
initial stream header.
2. If the TLS negotiation occurs between two servers,
communications MUST NOT proceed until the Domain Name System
(DNS) hostnames asserted by the servers have been resolved (see
Server-to-Server Communications (Section 14.4)).
3. When a receiving entity that complies with this specification
receives an initial stream header that includes the 'version'
attribute set to a value of "1.0", after sending a stream header
in reply (including the version flag) it MUST include a
<starttls/> element (qualified by the
'urn:ietf:params:xml:ns:xmpp-tls' namespace) along with the list
of other stream features it supports.
4. If the initiating entity chooses to use TLS, TLS negotiation
MUST be completed before proceeding to SASL negotiation; this
order of negotiation is required in order to help safeguard
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authentication information sent during SASL negotiation, as well
as to make it possible to base the use of the SASL EXTERNAL
mechanism on a certificate provided during prior TLS
negotiation.
5. During TLS negotiation, an entity MUST NOT send any white space
characters (matching production [3] content of [XML]) within the
root stream element as separators between elements (any white
space characters shown in the TLS examples below are included
for the sake of readability only); this prohibition helps to
ensure proper security layer byte precision.
6. The receiving entity MUST consider the TLS negotiation to have
begun immediately after sending the closing ">" character of the
<proceed/> element. The initiating entity MUST consider the TLS
negotiation to have begun immediately after receiving the
closing ">" character of the <proceed/> element from the
receiving entity.
7. The initiating entity MUST validate the certificate presented by
the receiving entity; see Certificate Validation (Section 14.2)
regarding certificate validation procedures.
8. Certificates MUST be checked against the hostname as provided by
the initiating entity (e.g., a user), not the hostname as
resolved via the Domain Name System; e.g., if the user or
certificate specifies a hostname of "example.com" but a DNS SRV
[SRV] lookup returned "im.example.com", the certificate MUST be
checked as "example.com". If a JID is represented in a
certificate, it SHOULD be encoded using the otherName choice of
the subjectAltName type along with a type-id of "xmpp" (as these
terms are profiled in [X509]).
9. Certificates MUST be checked against the hostname as provided by
the initiating entity (e.g., a user), not the hostname as
resolved via the Domain Name System; e.g., if the user or
certificate specifies a hostname of "example.com" but a DNS SRV
[SRV] lookup returned "im.example.com", the certificate MUST be
checked as "example.com". If a JID is represented in a
certificate, it SHOULD be encoded using the otherName choice of
the subjectAltName type along with a type-id of "xmpp" (as these
terms are profiled in [X509]).
10. If the TLS negotiation is successful, the receiving entity MUST
discard any knowledge obtained in an insecure manner from the
initiating entity before TLS takes effect.
11. If the TLS negotiation is successful, the initiating entity MUST
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discard any knowledge obtained in an insecure manner from the
receiving entity before TLS takes effect.
12. If the TLS negotiation is successful, the receiving entity MUST
NOT offer the STARTTLS extension to the initiating entity along
with the other stream features that are offered when the stream
is restarted.
13. If the TLS negotiation is successful, the initiating entity MUST
continue with SASL negotiation.
14. If the TLS negotiation results in failure, the receiving entity
MUST terminate both the XML stream and the underlying TCP
connection.
15. See Mandatory-to-Implement Technologies (Section 14.7) regarding
mechanisms that MUST be supported.
5.2 Narrative
When an initiating entity secures a stream with a receiving entity,
the steps involved are as follows:
1. The initiating entity opens a TCP connection and initiates the
stream by sending the opening XML stream header to the receiving
entity, including the 'version' attribute set to a value of
"1.0".
2. The receiving entity responds by opening a TCP connection and
sending an XML stream header to the initiating entity, including
the 'version' attribute set to a value of "1.0".
3. The receiving entity offers the STARTTLS extension to the
initiating entity by including it with the list of other
supported stream features (if TLS is required for interaction
with the receiving entity, it SHOULD signal that fact by
including a <required/> element as a child of the <starttls/>
element).
4. The initiating entity issues the STARTTLS command (i.e., a
<starttls/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-tls' namespace) to instruct the
receiving entity that it wishes to begin a TLS negotiation to
secure the stream.
5. The receiving entity MUST reply with either a <proceed/> element
or a <failure/> element qualified by the
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'urn:ietf:params:xml:ns:xmpp-tls' namespace. If the failure case
occurs, the receiving entity MUST terminate both the XML stream
and the underlying TCP connection. If the proceed case occurs,
the entities MUST attempt to complete the TLS negotiation over
the TCP connection and MUST NOT send any further XML data until
the TLS negotiation is complete.
6. The initiating entity and receiving entity attempt to complete a
TLS negotiation in accordance with [TLS].
7. If the TLS negotiation is unsuccessful, the receiving entity MUST
terminate the TCP connection (it is not necessary to send a
closing </stream> tag first, since the receiving entity and
initiating entity MUST consider the original stream to be closed
upon sending or receiving the <success/> element). If the TLS
negotiation is successful, the initiating entity MUST initiate a
new stream by sending an opening XML stream header to the
receiving entity.
8. Upon receiving the new stream header from the initiating entity,
the receiving entity MUST respond by sending a new XML stream
header to the initiating entity along with the available features
(but NOT including the STARTTLS feature).
5.3 Client-to-Server Example
The following example shows the data flow for a client securing a
stream using STARTTLS (note: the alternate steps shown below are
provided to illustrate the protocol for failure cases; they are not
exhaustive and would not necessarily be triggered by the data sent in
the example).
Step 1: Client initiates stream to server:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='example.com'
version='1.0'>
Step 2: Server responds by sending a stream tag to client:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='c2s_123'
from='example.com'
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version='1.0'>
Step 3: Server sends the STARTTLS extension to client along with
authentication mechanisms and any other stream features:
<stream:features>
<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'>
<required/>
</starttls>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
</mechanisms>
</stream:features>
Step 4: Client sends the STARTTLS command to server:
<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
Step 5: Server informs client to proceed:
<proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
Step 5 (alt): Server informs client that TLS negotiation has failed
and closes both stream and TCP connection:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
</stream:stream>
Step 6: Client and server attempt to complete TLS negotiation over
the existing TCP connection.
Step 7: If TLS negotiation is successful, client initiates a new
stream to server:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='example.com'
version='1.0'>
Step 7 (alt): If TLS negotiation is unsuccessful, Server2 closes TCP
connection.
Step 8: Server responds by sending a stream header to client along
with any available stream features:
<stream:stream
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xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
from='example.com'
id='c2s_234'
version='1.0'>
<stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
<mechanism>EXTERNAL</mechanism>
</mechanisms>
</stream:features>
Step 9: Client continues with SASL negotiation (Section 6).
5.4 Server-to-Server Example
The following example shows the data flow for two servers securing a
stream using STARTTLS (note: the alternate steps shown below are
provided to illustrate the protocol for failure cases; they are not
exhaustive and would not necessarily be triggered by the data sent in
the example).
Step 1: Server1 initiates stream to Server2:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
to='example.com'
version='1.0'>
Step 2: Server2 responds by sending a stream tag to Server1:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
from='example.com'
id='s2s_123'
version='1.0'>
Step 3: Server2 sends the STARTTLS extension to Server1 along with
authentication mechanisms and any other stream features:
<stream:features>
<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
<required/>
</starttls>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
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<mechanism>DIGEST-MD5</mechanism>
<mechanism>KERBEROS_V4</mechanism>
</mechanisms>
</stream:features>
Step 4: Server1 sends the STARTTLS command to Server2:
<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
Step 5: Server2 informs Server1 to proceed:
<proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
Step 5 (alt): Server2 informs Server1 that TLS negotiation has failed
and closes stream:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
</stream:stream>
Step 6: Server1 and Server2 attempt to complete TLS negotiation via
TCP.
Step 7: If TLS negotiation is successful, Server1 initiates a new
stream to Server2:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
to='example.com'
version='1.0'>
Step 7 (alt): If TLS negotiation is unsuccessful, server closes TCP
connection.
Step 8: Server2 responds by sending a stream header to Server1 along
with any available stream features:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
from='example.com'
id='s2s_234'
version='1.0'>
<stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>KERBEROS_V4</mechanism>
<mechanism>EXTERNAL</mechanism>
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</mechanisms>
</stream:features>
Step 9: Server1 continues with SASL negotiation (Section 6).
6. Use of SASL
6.1 Overview
XMPP includes a method for authenticating a stream by means of an
XMPP-specific profile of the Simple Authentication and Security Layer
(SASL) protocol [SASL]. SASL provides a generalized method for
adding authentication support to connection-based protocols, and XMPP
uses a generic XML namespace profile for SASL that conforms to the
profiling requirements of [SASL].
The following rules apply:
1. If the SASL negotiation occurs between two servers,
communications MUST NOT proceed until the Domain Name System
(DNS) hostnames asserted by the servers have been resolved (see
Server-to-Server Communications (Section 14.4)).
2. If the initiating entity is capable of SASL negotiation, it MUST
include the 'version' attribute set to a value of "1.0" in the
initial stream header.
3. If the receiving entity is capable of SASL negotiation, it MUST
send one or more authentication mechanisms within a <mechanisms/
> element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl'
namespace in reply to the opening stream tag received from the
initiating entity (if the opening stream tag included the
'version' attribute set to a value of "1.0").
4. During SASL negotiation, an entity MUST NOT send any white space
characters (matching production [3] content of [XML]) within the
root stream element as separators between elements (any white
space characters shown in the SASL examples below are included
for the sake of readability only); this prohibition helps to
ensure proper security layer byte precision.
5. Any character data contained within the XML elements used during
SASL negotiation MUST be encoded using base64, where the
encoding adheres to the definition in Section 3 of RFC 3548
[BASE64].
6. If provision of a "simple username" is supported by the selected
SASL mechanism (e.g., this is supported by the DIGEST-MD5 and
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CRAM-MD5 mechanisms but not by the EXTERNAL and GSSAPI
mechanisms), during authentication the initiating entity SHOULD
provide its sending domain (in the case of server-to-server
communications) or registered account name (in the case of
client-to-server communications) as the simple username.
7. If the initiating entity wishes to act on behalf of another
entity and the selected SASL mechanism supports transmission of
an authorization identity, the initiating entity MUST provide an
authorization identity during SASL negotiation. If the
initiating entity does not wish to act on behalf of another
entity, it MUST NOT provide an authorization identity. As
specified in [SASL], the initiating entity MUST NOT provide an
authorization identity unless the authorization identity is
different from the default authorization identity derived from
the authentication identity as described in [SASL]. If
provided, the value of the authorization identity MUST be of the
form <domain> (i.e., a domain identifier only) for servers and
of the form <node@domain> (i.e., node identifier and domain
identifier) for clients.
8. Upon successful SASL negotiation that involves negotiation of a
security layer, the receiving entity MUST discard any knowledge
obtained from the initiating entity which was not obtained from
the SASL negotiation itself.
9. Upon successful SASL negotiation that involves negotiation of a
security layer, the initiating entity MUST discard any knowledge
obtained from the receiving entity which was not obtained from
the SASL negotiation itself.
10. See Mandatory-to-Implement Technologies (Section 14.7) regarding
mechanisms that MUST be supported.
6.2 Narrative
When an initiating entity authenticates with a receiving entity, the
steps involved are as follows:
1. The initiating entity requests SASL authentication by including
the 'version' attribute in the opening XML stream header sent to
the receiving entity, with the value set to "1.0".
2. After sending an XML stream header in reply, the receiving entity
sends a list of available SASL authentication mechanisms; each of
these is a <mechanism/> element included as a child within a
<mechanisms/> container element qualified by the
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'urn:ietf:params:xml:ns:xmpp-sasl' namespace, which in turn is a
child of a <features/> element in the streams namespace. If Use
of TLS (Section 5) needs to be established before a particular
authentication mechanism may be used, the receiving entity MUST
NOT provide that mechanism in the list of available SASL
authentication mechanisms prior to TLS negotiation. If the
initiating entity presents a valid certificate during prior TLS
negotiation, the receiving entity SHOULD offer the SASL EXTERNAL
mechanism to the initiating entity during SASL negotiation (refer
to [SASL]), although the EXTERNAL mechanism MAY be offered under
other circumstances as well.
3. The initiating entity selects a mechanism by sending an <auth/>
element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl'
namespace to the receiving entity and including an appropriate
value for the 'mechanism' attribute; this element MAY contain
character data (in SASL terminology, the "initial response") if
the mechanism supports or requires it. If the initiating entity
selects the EXTERNAL mechanism for authentication and presented a
certificate during prior TLS negotiation, the authentication
credentials SHOULD be taken from that certificate.
4. If necessary, the receiving entity challenges the initiating
entity by sending a <challenge/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the initiating
entity; this element MAY contain character data (which MUST be
computed in accordance with the definition of the SASL mechanism
chosen by the initiating entity).
5. The initiating entity responds to the challenge by sending a
<response/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the receiving
entity; this element MAY contain character data (which MUST be
computed in accordance with the definition of the SASL mechanism
chosen by the initiating entity).
6. If necessary, the receiving entity sends more challenges and the
initiating entity sends more responses.
This series of challenge/response pairs continues until one of three
things happens:
1. The initiating entity aborts the handshake by sending an <abort/>
element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl'
namespace to the receiving entity. Upon receiving an <abort/>
element, the receiving entity SHOULD allow a configurable but
reasonable number of retries (at least 2), after which it MUST
terminate the TCP connection; this allows the initiating entity
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(e.g., an end-user client) to tolerate incorrectly-provided
credentials (e.g., a mistyped password) without being forced to
reconnect.
2. The receiving entity reports failure of the handshake by sending
a <failure/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the initiating
entity (the particular cause of failure SHOULD be communicated in
an appropriate child element of the <failure/> element as defined
under SASL Errors (Section 6.4)). If the failure case occurs,
the receiving entity SHOULD allow a configurable but reasonable
number of retries (at least 2), after which it MUST terminate the
TCP connection; this allows the initiating entity (e.g., an
end-user client) to tolerate incorrectly-provided credentials
(e.g., a mistyped password) without being forced to reconnect.
3. The receiving entity reports success of the handshake by sending
a <success/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the initiating
entity; this element MAY contain character data (in SASL
terminology, "additional data with success") if required by the
chosen SASL mechanism. Upon receiving the <success/> element,
the initiating entity MUST initiate a new stream by sending an
opening XML stream header to the receiving entity (it is not
necessary to send a closing </stream> tag first, since the
receiving entity and initiating entity MUST consider the original
stream to be closed upon sending or receiving the <success/>
element). Upon receiving the new stream header from the
initiating entity, the receiving entity MUST respond by sending a
new XML stream header to the initiating entity, along with any
available features (but NOT including the STARTTLS feature) or an
empty <features/> element (to signify that no additional features
are available); any such additional features not defined herein
MUST be defined by the relevant extension to XMPP.
6.3 SASL Definition
The profiling requirements of [SASL] require that the following
information be supplied by a protocol definition:
service name: "xmpp"
initiation sequence: After the initiating entity provides an opening
XML stream header and the receiving entity replies in kind, the
receiving entity provides a list of acceptable authentication
methods. The initiating entity chooses one method from the list
and sends it to the receiving entity as the value of the
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'mechanism' attribute possessed by an <auth/> element, optionally
including an initial response to avoid a round trip.
exchange sequence: Challenges and responses are carried through the
exchange of <challenge/> elements from receiving entity to
initiating entity and <response/> elements from initiating entity
to receiving entity. The receiving entity reports failure by
sending a <failure/> element and success by sending a <success/>
element; the initiating entity aborts the exchange by sending an
<abort/> element. Upon successful negotiation, both sides
consider the original XML stream to be closed and new stream
headers are sent by both entities.
security layer negotiation: The security layer takes effect
immediately after sending the closing ">" character of the
<success/> element for the receiving entity, and immediately after
receiving the closing ">" character of the <success/> element for
the initiating entity. The order of layers is first [TCP], then
[TLS], then [SASL], then XMPP.
use of the authorization identity: The authorization identity may be
used by xmpp to denote the <node@domain> of a client or the
sending <domain> of a server.
6.4 SASL Errors
The following SASL-related error conditions are defined:
o <aborted/> -- The receiving entity acknowledges an <abort/>
element sent by the initiating entity; sent in reply to the
<abort/> element.
o <incorrect-encoding/> -- The data provided by the initiating
entity could not be processed because the [BASE64] encoding is
incorrect (e.g., because the encoding does not adhere to the the
definition in Section 3 of [BASE64]); sent in reply to a
<response/> element or an <auth/> element with initial challenge
data.
o <invalid-authzid/> -- The authzid provided by the initiating
entity is invalid, either because it is incorrectly formatted or
because the initiating entity does not have permissions to
authorize that ID; sent in reply to a <response/> element or an
<auth/> element with initial challenge data.
o <invalid-mechanism/> -- The initiating entity did not provide a
mechanism or requested a mechanism that is not supported by the
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receiving entity; sent in reply to an <auth/> element.
o <mechanism-too-weak/> -- The mechanism requested by the initiating
entity is weaker than server policy permits for that initiating
entity; sent in reply to a <response/> element or an <auth/>
element with initial challenge data.
o <not-authorized/> -- The authentication failed because the
initiating entity did not provide valid credentials (this includes
but is not limited to the case of an unknown username); sent in
reply to a <response/> element or an <auth/> element with initial
challenge data.
o <temporary-auth-failure/> -- The authentication failed because of
a temporary error condition within the receiving entity; sent in
reply to an <auth/> element or <response/> element.
6.5 Client-to-Server Example
The following example shows the data flow for a client authenticating
with a server using SASL, normally after successful TLS negotiation
(note: the alternate steps shown below are provided to illustrate the
protocol for failure cases; they are not exhaustive and would not
necessarily be triggered by the data sent in the example).
Step 1: Client initiates stream to server:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='example.com'
version='1.0'>
Step 2: Server responds with a stream tag sent to client:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='c2s_234'
from='example.com'
version='1.0'>
Step 3: Server informs client of available authentication mechanisms:
<stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
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<mechanism>PLAIN</mechanism>
</mechanisms>
</stream:features>
Step 4: Client selects an authentication mechanism:
<auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
mechanism='DIGEST-MD5'/>
Step 5: Server sends a [BASE64] encoded challenge to client:
<challenge xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
cmVhbG09InNvbWVyZWFsbSIsbm9uY2U9Ik9BNk1HOXRFUUdtMmhoIixxb3A9ImF1dGgi
LGNoYXJzZXQ9dXRmLTgsYWxnb3JpdGhtPW1kNS1zZXNzCg==
</challenge>
The decoded challenge is:
realm="somerealm",nonce="OA6MG9tEQGm2hh",\
qop="auth",charset=utf-8,algorithm=md5-sess
Step 5 (alt): Server returns error to client:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<incorrect-encoding/>
</failure>
</stream:stream>
Step 6: Client sends a [BASE64] encoded response to the challenge:
<response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
dXNlcm5hbWU9InNvbWVub2RlIixyZWFsbT0ic29tZXJlYWxtIixub25jZT0i
T0E2TUc5dEVRR20yaGgiLGNub25jZT0iT0E2TUhYaDZWcVRyUmsiLG5jPTAw
MDAwMDAxLHFvcD1hdXRoLGRpZ2VzdC11cmk9InhtcHAvZXhhbXBsZS5jb20i
LHJlc3BvbnNlPWQzODhkYWQ5MGQ0YmJkNzYwYTE1MjMyMWYyMTQzYWY3LGNo
YXJzZXQ9dXRmLTgK
</response>
The decoded response is:
username="somenode",realm="somerealm",\
nonce="OA6MG9tEQGm2hh",cnonce="OA6MHXh6VqTrRk",\
nc=00000001,qop=auth,digest-uri="xmpp/example.com",\
response=d388dad90d4bbd760a152321f2143af7,charset=utf-8
Step 7: Server sends another [BASE64] encoded challenge to client:
<challenge xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
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cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZAo=
</challenge>
The decoded challenge is:
rspauth=ea40f60335c427b5527b84dbabcdfffd
Step 7 (alt): Server returns error to client:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<temporary-auth-failure/>
</failure>
</stream:stream>
Step 8: Client responds to the challenge:
<response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
Step 9: Server informs client of successful authentication:
<success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
Step 9 (alt): Server informs client of failed authentication:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<temporary-auth-failure/>
</failure>
</stream:stream>
Step 10: Client initiates a new stream to server:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='example.com'
version='1.0'>
Step 11: Server responds by sending a stream header to client along
with any additional features (or an empty features element):
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='c2s_345'
from='example.com'
version='1.0'>
<stream:features>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/>
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<session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
</stream:features>
6.6 Server-to-Server Example
The following example shows the data flow for a server authenticating
with another server using SASL, normally after successful TLS
negotiation (note: the alternate steps shown below are provided to
illustrate the protocol for failure cases; they are not exhaustive
and would not necessarily be triggered by the data sent in the
example).
Step 1: Server1 initiates stream to Server2:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
to='example.com'
version='1.0'>
Step 2: Server2 responds with a stream tag sent to Server1:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
from='example.com'
id='s2s_234'
version='1.0'>
Step 3: Server2 informs Server1 of available authentication
mechanisms:
<stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>KERBEROS_V4</mechanism>
</mechanisms>
</stream:features>
Step 4: Server1 selects an authentication mechanism:
<auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
mechanism='DIGEST-MD5'/>
Step 5: Server2 sends a [BASE64] encoded challenge to Server1:
<challenge xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
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dXNlcm5hbWU9ImV4YW1wbGUuY29tIixyZWFsbT0ic29tZXJlYWxtIixub25j
ZT0iT0E2TUc5dEVRR20yaGgiLHFvcD0iYXV0aCIsY2hhcnNldD11dGYtOCxh
bGdvcml0aG09bWQ1LXNlc3MK
</challenge>
The decoded challenge is:
username="example.com",realm="somerealm",\
nonce="OA6MG9tEQGm2hh",qop="auth",\
charset=utf-8,algorithm=md5-sess
Step 5 (alt): Server2 returns error to Server1:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<incorrect-encoding/>
</failure>
</stream:stream>
Step 6: Server1 sends a [BASE64] encoded response to the challenge:
<response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
dXNlcm5hbWU9ImV4YW1wbGUuY29tIixyZWFsbT0ic29tZXJlYWxtIixub25j
ZT0iT0E2TUc5dEVRR20yaGgiLGNub25jZT0iT0E2TUhYaDZWcVRyUmsiLG5j
PTAwMDAwMDAxLHFvcD1hdXRoLGRpZ2VzdC11cmk9InhtcHAvZXhhbXBsZS5j
b20iLHJlc3BvbnNlPWQzODhkYWQ5MGQ0YmJkNzYwYTE1MjMyMWYyMTQzYWY3
LGNoYXJzZXQ9dXRmLTgK
</response>
The decoded response is:
username="example.com",realm="somerealm",\
nonce="OA6MG9tEQGm2hh",cnonce="OA6MHXh6VqTrRk",\
nc=00000001,qop=auth,digest-uri="xmpp/example.com",\
response=d388dad90d4bbd760a152321f2143af7,charset=utf-8
Step 7: Server2 sends another [BASE64] encoded challenge to Server1:
<challenge xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZAo=
</challenge>
The decoded challenge is:
rspauth=ea40f60335c427b5527b84dbabcdfffd
Step 7 (alt): Server2 returns error to Server1:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
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<invalid-authzid/>
</failure>
</stream:stream>
Step 8: Server1 responds to the challenge:
<response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
Step 8 (alt): Server1 aborts negotiation:
<abort xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
Step 9: Server2 informs Server1 of successful authentication:
<success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
Step 9 (alt): Server2 informs Server1 of failed authentication:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<aborted/>
</failure>
</stream:stream>
Step 10: Server1 initiates a new stream to Server2:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
to='example.com'
version='1.0'>
Step 11: Server2 responds by sending a stream header to Server1 along
with any additional features (or an empty features element):
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
from='example.com'
id='s2s_345'
version='1.0'>
<stream:features/>
7. Resource Binding
After SASL negotiation (Section 6) with the receiving entity, the
initiating entity MAY want or need to bind a specific resource to
that stream. In general this applies only to clients: in order to
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conform to the addressing format (Section 3) and stanza delivery
rules (Section 10) specified herein, there MUST be a resource
identifier associated with the <node@domain> of the client (which is
either generated by the server or provided by the client
application); this ensures that the address for use over that stream
is a "full JID" of the form <node@domain/resource>.
Upon receiving a success indication within the SASL negotiation, the
client MUST send a new stream header to the server, to which the
server MUST respond with a stream header as well as a list of
available stream features. Specifically, if the server requires the
client to bind a resource to the stream after successful SASL
negotiation, it MUST include an empty <bind/> element qualified by
the 'urn:ietf:params:xml:ns:xmpp-bind' namespace in the stream
features list it presents to the client upon sending the header for
the response stream sent after successful SASL negotiation (but not
before):
Server advertises resource binding feature to client:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='c2s_345'
from='example.com'
version='1.0'>
<stream:features>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/>
</stream:features>
Upon being so informed that resource binding is required, the client
MUST bind a resource to the stream by sending to the server an IQ
stanza of type "set" (see IQ Semantics (Section 9.2.3)) containing
data qualified by the 'urn:ietf:params:xml:ns:xmpp-bind' namespace.
If the client wishes to allow the server to generate the resource
identifier on its behalf, it sends an IQ stanza of type "set" that
contains an empty <bind/> element:
Client asks server to bind a resource:
<iq type='set' id='bind_1'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/>
</iq>
A server that supports resource binding MUST be able to generate a
resource identifier on behalf of a client. A resource identifier
generated by the server MUST be unique for that <node@domain>.
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If the client wishes to specify the resource identifier, it sends an
IQ stanza of type "set" that contains the desired resource identifier
as the CDATA of a <resource/> element that is a child of the <bind/>
element:
Client binds a resource:
<iq type='set' id='bind_2'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<resource>someresource</resource>
</bind>
</iq>
Once the server has generated a resource identifier for the client or
accepted the resource identifier provided by the client, it MUST
return an IQ stanza of type "result" to the client, which MUST
include a <jid/> child element that specifies the full JID for the
connected resource as determined by the server:
Server informs client of successful resource binding:
<iq type='result' id='bind_2'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<jid>somenode@example.com/someresource</jid>
</bind>
</iq>
A server is NOT REQUIRED to accept the resource identifier provided
by the client, and MAY override it with a resource identifier that
the server generates; in this case, the server SHOULD NOT return a
stanza error (e.g., <forbidden/>) to the client but instead SHOULD
communicate the generated resource identifier to the client in the IQ
result as shown above.
When a client supplies a resource identifier, the following stanza
error conditions are possible (see Stanza Errors (Section 9.3)):
o The provided resource identifier cannot be processed by the server
in accordance with Resourceprep (Appendix B).
o The client is not allowed to bind a resource to the stream (e.g.,
because the client has reached a limit on the number of connected
resources allowed).
o The provided resource identifier is already in use but the server
does not allow binding of multiple connected resources with the
same identifier.
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The protocol for these error conditions is shown below.
Resource identifier cannot be processed:
<iq type='error' id='bind_2'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<resource>someresource</resource>
</bind>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
Client is not allowed to bind a resource:
<iq type='error' id='bind_2'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<resource>someresource</resource>
</bind>
<error type='cancel'>
<not-allowed xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
Resource identifier is in use:
<iq type='error' id='bind_2'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<resource>someresource</resource>
</bind>
<error type='cancel'>
<conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
8. Server Dialback
8.1 Overview
The Jabber protocols from which XMPP was adapted include a "server
dialback" method for protecting against domain spoofing, thus making
it more difficult to spoof XML stanzas (see Server-to-Server
Communications (Section 14.4) regarding this method's security
characteristics). Server dialback also makes it easier to deploy
systems in which outbound messages and inbound messages are handled
by different machines for the same domain. Server dialback is not a
security mechanism, and domains requiring robust security SHOULD use
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TLS and SASL; see Server-to-Server Communications (Section 14.4) for
details.
The server dialback method is made possible by the existence of the
Domain Name System (DNS), since one server can (normally) discover
the authoritative server for a given domain. Because dialback depends
on DNS, inter-domain communications MUST NOT proceed until the Domain
Name System (DNS) hostnames asserted by the servers have been
resolved (see Server-to-Server Communications (Section 14.4)).
The method for generating and verifying the keys used in server
dialback MUST take into account the hostnames being used, the stream
ID generated by the receiving server, and a secret known by the
authoritative server's network. The stream ID is security-critical in
server dialback and therefore MUST be both unpredictable and
non-repeating.
Any error that occurs during dialback negotiation MUST be considered
a stream error, resulting in termination of the stream and of the
underlying TCP connection. The possible error conditions are
specified in the protocol description below.
The following terminology applies:
o Originating Server -- the server that is attempting to establish a
connection between two domains.
o Receiving Server -- the server that is trying to authenticate that
Originating Server represents the domain which it claims to be.
o Authoritative Server -- the server that answers to the DNS
hostname asserted by Originating Server; for basic environments
this will be Originating Server, but it could be a separate
machine in Originating Server's network.
8.2 Order of Events
The following is a brief summary of the order of events in dialback:
1. Originating Server establishes a connection to Receiving Server.
2. Originating Server sends a 'key' value over the connection to
Receiving Server.
3. Receiving Server establishes a connection to Authoritative
Server.
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4. Receiving Server sends the same 'key' value to Authoritative
Server.
5. Authoritative Server replies that key is valid or invalid.
6. Receiving Server informs Originating Server whether it is
authenticated or not.
We can represent this flow of events graphically as follows:
Originating Receiving
Server Server
----------- ---------
| |
| establish connection |
| ----------------------> |
| |
| send stream header |
| ----------------------> |
| |
| send stream header |
| <---------------------- |
| | Authoritative
| send dialback key | Server
| ----------------------> | -------------
| | |
| establish connection |
| ----------------------> |
| |
| send stream header |
| ----------------------> |
| |
| send stream header |
| <---------------------- |
| |
| send verify request |
| ----------------------> |
| |
| send verify response |
| <---------------------- |
|
| report dialback result |
| <---------------------- |
| |
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8.3 Protocol
The detailed protocol interaction between the servers is as follows:
1. Originating Server establishes TCP connection to Receiving
Server.
2. Originating Server sends a stream header to Receiving Server:
<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'>
Note: The 'to' and 'from' attributes are NOT REQUIRED on the
root stream element. The inclusion of the xmlns:db namespace
declaration with the name shown indicates to Receiving Server
that Originating Server supports dialback. If the namespace
name is incorrect, then Receiving Server MUST generate an
<invalid-namespace/> stream error condition and terminate both
the XML stream and the underlying TCP connection.
3. Receiving Server SHOULD send a stream header back to Originating
Server, including a unique ID for this interaction:
<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'
id='457F9224A0...'>
Note: The 'to' and 'from' attributes are NOT REQUIRED on the
root stream element. If the namespace name is incorrect, then
Originating Server MUST generate an <invalid-namespace/> stream
error condition and terminate both the XML stream and the
underlying TCP connection. Note well that Receiving Server is
NOT REQUIRED to reply and MAY silently terminate the XML stream
and underlying TCP connection depending on security policies in
place; however, if Receiving Server desires to proceed, it MUST
sent a stream header back to Originating Server.
4. Originating Server sends a dialback key to Receiving Server:
<db:result
to='Receiving Server'
from='Originating Server'>
98AF014EDC0...
</db:result>
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Note: This key is not examined by Receiving Server, since
Receiving Server does not keep information about Originating
Server between sessions. The key generated by Originating
Server MUST be based in part on the value of the ID provided by
Receiving Server in the previous step, and in part on a secret
shared by Originating Server and Authoritative Server. If the
value of the 'to' address does not match a hostname recognized
by Receiving Server, then Receiving Server MUST generate a
<host-unknown/> stream error condition and terminate both the
XML stream and the underlying TCP connection. If the value of
the 'from' address matches a domain with which Receiving Server
already has an established connection, then Receiving Server
MUST maintain the existing connection until it validates whether
the new connection is legitimate; additionally, Receiving Server
MAY choose to generate a <not-authorized/> stream error
condition for the new connection and then terminate both the XML
stream and the underlying TCP connection related to the new
request.
5. Receiving Server establishes a TCP connection back to the domain
name asserted by Originating Server, as a result of which it
connects to Authoritative Server. (Note: As an optimization, an
implementation MAY reuse an existing trusted connection here
rather than opening a new TCP connection.)
6. Receiving Server sends Authoritative Server a stream header:
<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'>
Note: The 'to' and 'from' attributes are NOT REQUIRED on the
root stream element. If the namespace name is incorrect, then
Authoritative Server MUST generate an <invalid-namespace/>
stream error condition and terminate both the XML stream and the
underlying TCP connection.
7. Authoritative Server sends Receiving Server a stream header:
<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'
id='1251A342B...'>
Note: If the namespace name is incorrect, then Receiving Server
MUST generate an <invalid-namespace/> stream error condition and
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terminate both the XML stream and the underlying TCP connection
between it and Authoritative Server. If a stream error occurs
between Receiving Server and Authoritative Server, then
Receiving Server MUST generate a <remote-connection-failed/>
stream error condition and terminate both the XML stream and the
underlying TCP connection between it and Originating Server.
8. Receiving Server sends Authoritative Server a stanza requesting
that Authoritative Server verify a key:
<db:verify
from='Receiving Server'
to='Originating Server'
id='457F9224A0...'>
98AF014EDC0...
</db:verify>
Note: Passed here are the hostnames, the original identifier
from Receiving Server's stream header to Originating Server in
Step 3, and the key that Originating Server sent to Receiving
Server in Step 4. Based on this information as well as shared
secret information within the Authoritative Server's network,
the key is verified. Any verifiable method MAY be used to
generate the key. If the value of the 'to' address does not
match a hostname recognized by Authoritative Server, then
Authoritative Server MUST generate a <host-unknown/> stream
error condition and terminate both the XML stream and the
underlying TCP connection. If the value of the 'from' address
does not match the hostname represented by Receiving Server when
opening the TCP connection (or any validated domain), then
Authoritative Server MUST generate an <invalid-from/> stream
error condition and terminate both the XML stream and the
underlying TCP connection.
9. Authoritative Server sends a stanza back to Receiving Server
verifying whether the key was valid or invalid:
<db:verify
from='Originating Server'
to='Receiving Server'
type='valid'
id='457F9224A0...'/>
or
<db:verify
from='Originating Server'
to='Receiving Server'
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type='invalid'
id='457F9224A0...'/>
Note: If the ID does not match that provided by Receiving Server
in Step 3, then Receiving Server MUST generate an <invalid-id/>
stream error condition and terminate both the XML stream and the
underlying TCP connection. If the value of the 'to' address
does not match a hostname recognized by Receiving Server, then
Receiving Server MUST generate a <host-unknown/> stream error
condition and terminate both the XML stream and the underlying
TCP connection. If the value of the 'from' address does not
match the hostname represented by Originating Server when
opening the TCP connection (or any validated domain), then
Receiving Server MUST generate an <invalid-from/> stream error
condition and terminate both the XML stream and the underlying
TCP connection. After returning the verification to Receiving
Server, Authoritative Server SHOULD terminate the stream between
them.
10. Receiving Server informs Originating Server of the result:
<db:result
from='Receiving Server'
to='Originating Server'
type='valid'/>
Note: At this point the connection has either been validated via
a type='valid', or reported as invalid. If the connection is
invalid, then Receiving Server MUST terminate both the XML
stream and the underlying TCP connection. If the connection is
validated, data can be sent by Originating Server and read by
Receiving Server; before that, all data stanzas sent to
Receiving Server SHOULD be silently dropped.
Even if dialback negotiation is successful, a server MUST verify that
all XML stanzas received from the other server include a 'from'
attribute and a 'to' attribute; if a stanza does not meet this
restriction, the server that receives the stanza MUST generate an
<improper-addressing/> stream error condition and terminate both the
XML stream and the underlying TCP connection. Furthermore, a server
MUST verify that the 'from' attribute of stanzas received from the
other server includes a validated domain for the stream; if a stanza
does not meet this restriction, the server that receives the stanza
MUST generate an <invalid-from/> stream error condition and terminate
both the XML stream and the underlying TCP connection. Both of these
checks help to prevent spoofing related to particular stanzas.
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9. XML Stanzas
After TLS negotiation (Section 5) if desired, SASL negotiation
(Section 6), and Resource Binding (Section 7) if necessary, XML
stanzas can be sent over the streams. Three kinds of XML stanza are
defined for the 'jabber:client' and 'jabber:server' namespaces:
<message/>, <presence/>, and <iq/>. In addition, there are five
common attributes for these kinds of stanza. These common
attributes, as well as the basic semantics of the three stanza kinds,
are defined herein; more detailed information regarding the syntax of
XML stanzas in relation to instant messaging and presence
applications is provided in [XMPP-IM].
9.1 Common Attributes
The following five attributes are common to message, presence, and IQ
stanzas:
9.1.1 to
The 'to' attribute specifies the JID of the intended recipient for
the stanza.
In the 'jabber:client' namespace, a stanza SHOULD possess a 'to'
attribute, although a stanza sent from a client to a server for
handling by that server (e.g., presence sent to the server for
broadcasting to other entities) SHOULD NOT possess a 'to' attribute.
In the 'jabber:server' namespace, a stanza MUST possess a 'to'
attribute; if a server receives a stanza that does not meet this
restriction, it MUST generate an <improper-addressing/> stream error
condition and terminate both the XML stream and the underlying TCP
connection with the offending server.
If the value of the 'to' attribute is invalid or cannot be contacted,
the entity discovering that fact (usually the sender's or recipient's
server) MUST return an appropriate error to the sender, setting the
'from' attribute of the error stanza to the value provided in the
'to' attribute of the offending stanza.
9.1.2 from
The 'from' attribute specifies the JID of the sender.
When a server receives an XML stanza within the context of an
authenticated stream qualified by the 'jabber:client' namespace, it
MUST do one of the following:
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1. validate that the value of the 'from' attribute provided by the
client is that of a connected resource for the associated entity
2. add a 'from' address to the stanza whose value is the full JID
(<node@domain/resource>) determined by the server for the
connected resource that generated the stanza (see Determination
of Addresses (Section 3.5))
If a client attempts to send an XML stanza for which the value of the
'from' attribute does not match one of the connected resources for
that entity, the server SHOULD return an <invalid-from/> stream error
to the client. If a client attempts to send an XML stanza over a
stream that is not yet authenticated, the server SHOULD return a
<not-authorized/> stream error to the client. If generated, both of
these conditions MUST result in closing of the stream and termination
of the underlying TCP connection; this helps to prevent a denial of
service attack launched from a rogue client.
When a server generates a stanza from the server itself for delivery
to a connected client (e.g., in the context of data storage services
provided by the server on behalf of the client), the stanza MUST
either (1) not include a 'from' attribute or (2) include a 'from'
attribute whose value is the account's bare JID (<node@domain>) or
client's full JID (<node@domain/resource>). A server MUST NOT send
to the client a stanza without a 'from' attribute if the stanza was
not generated by the server itself. When a client receives a stanza
that does not include a 'from' attribute, it MUST assume that the
stanza is from the server to which the client is connected.
In the 'jabber:server' namespace, a stanza MUST possess a 'from'
attribute; if a server receives a stanza that does not meet this
restriction, it MUST generate an <improper-addressing/> stream error
condition. Furthermore, the domain identifier portion of the JID
contained in the 'from' attribute MUST match the hostname (or any
validated domain) of the sending server as communicated in the SASL
negotiation or dialback negotiation; if a server receives a stanza
that does not meet this restriction, it MUST generate an
<invalid-from/> stream error condition. Both of these conditions
MUST result in closing of the stream and termination of the
underlying TCP connection; this helps to prevent a denial of service
attack launched from a rogue server.
9.1.3 id
The optional 'id' attribute MAY be used by a sending entity for
internal tracking of stanzas that it sends and receives (especially
for tracking the request-response interaction inherent in the
semantics of IQ stanzas). The value of the 'id' attribute is NOT
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REQUIRED to be unique either globally, within a domain, or within a
stream. The semantics of IQ stanzas impose additional restrictions;
see IQ Semantics (Section 9.2.3).
9.1.4 type
The 'type' attribute specifies detailed information about the purpose
or context of the message, presence, or IQ stanza. The particular
allowable values for the 'type' attribute vary depending on whether
the stanza is a message, presence, or IQ; the values for message and
presence stanzas are specific to instant messaging and presence
applications and therefore are defined in [XMPP-IM], whereas the
values for IQ stanzas specify the role of an IQ stanza in a
structured request-response "conversation" and thus are defined under
IQ Semantics (Section 9.2.3) below. The only 'type' value common to
all three stanzas is "error", for which see Stanza Errors (Section
9.3).
9.1.5 xml:lang
A stanza SHOULD possess an 'xml:lang' attribute (as defined in
Section 2.12 of [XML]) if the stanza contains XML character data that
is intended to be presented to a human user (as explained in RFC 2277
[CHARSET], "internationalization is for humans"). The value of the
'xml:lang' attribute specifies the default language of any such
human-readable XML character data, which MAY be overridden by the
'xml:lang' attribute of a specific child element. If a stanza does
not possess an 'xml:lang' attribute, an implementation MUST assume
that the default language is that specified for the stream as defined
under Stream Attributes (Section 4.2) above. The value of the
'xml:lang' attribute MUST be an NMTOKEN and MUST conform to the
format defined in RFC 3066 [LANGTAGS].
9.2 Basic Semantics
9.2.1 Message Semantics
The <message/> stanza kind can be seen as a "push" mechanism whereby
one entity pushes information to another entity, similar to the
communications that occur in a system such as email. All message
stanzas SHOULD possess a 'to' attribute that specifies the intended
recipient of the message; upon receiving such a stanza, a server
SHOULD route or deliver it to the intended recipient (see Server
Rules for Handling XML Stanzas (Section 10) for general routing and
delivery rules related to XML stanzas).
9.2.2 Presence Semantics
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The <presence/> element can be seen as a basic broadcast or
"publish-subscribe" mechanism, whereby multiple entities receive
information (in this case, presence information) about an entity to
which they have subscribed. In general, a publishing entity SHOULD
send a presence stanza with no 'to' attribute, in which case the
server to which the entity is connected SHOULD broadcast or multiplex
that stanza to all subscribing entities. However, a publishing
entity MAY also send a presence stanza with a 'to' attribute, in
which case the server SHOULD route or deliver that stanza to the
intended recipient. See Server Rules for Handling XML Stanzas
(Section 10) for general routing and delivery rules related to XML
stanzas, and [XMPP-IM] for presence-specific rules in the context of
an instant messaging and presence application.
9.2.3 IQ Semantics
Info/Query, or IQ, is a request-response mechanism, similar in some
ways to [HTTP]. The semantics of IQ enable an entity to make a
request of, and receive a response from, another entity. The data
content of the request and response is defined by the namespace
declaration of a direct child element of the IQ element, and the
interaction is tracked by the requesting entity through use of the
'id' attribute. Thus IQ interactions follow a common pattern of
structured data exchange such as get/result or set/result (although
an error may be returned in reply to a request if appropriate):
Requesting Responding
Entity Entity
---------- ----------
| |
| <iq type='get' id='1'> |
| ------------------------> |
| |
| <iq type='result' id='1'> |
| <------------------------ |
| |
| <iq type='set' id='2'> |
| ------------------------> |
| |
| <iq type='error' id='2'> |
| <------------------------ |
| |
In order to enforce these semantics, the following rules apply:
1. The 'id' attribute is REQUIRED for IQ stanzas.
2. The 'type' attribute is REQUIRED for IQ stanzas. The value MUST
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be one of the following:
3.
* get -- The stanza is a request for information or
requirements.
* set -- The stanza provides required data, sets new values, or
replaces existing values.
* result -- The stanza is a response to a successful get or set
request.
* error -- An error has occurred regarding processing or
delivery of a previously-sent get or set (see Stanza Errors
(Section 9.3)).
4. An entity that receives an IQ request of type "get" or "set" MUST
reply with an IQ response of type "result" or "error" (which
response MUST preserve the 'id' attribute of the request).
5. An entity that receives a stanza of type "result" or "error" MUST
NOT respond to the stanza by sending a further IQ response of
type "result" or "error"; however, as shown above, the requesting
entity MAY send another request (e.g., an IQ of type "set" in
order to provide required information discovered through a get/
result pair).
6. An IQ stanza of type "get" or "set" MUST contain one and only one
child element (properly-namespaced as defined in [XMPP-IM]) that
specifies the semantics of the particular request or response.
7. An IQ stanza of type "result" MUST include zero or one child
elements.
8. An IQ stanza of type "error" SHOULD include the child element
contained in the associated "get" or "set" and MUST include an
<error/> child; for details, see Stanza Errors (Section 9.3).
9.3 Stanza Errors
Stanza-related errors are handled in a manner similar to stream
errors (Section 4.6). However, unlike stream errors, stanza errors
are recoverable; therefore error stanzas include hints regarding
actions that the original sender can take in order to remedy the
error.
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9.3.1 Rules
The following rules apply to stanza-related errors:
o The receiving or processing entity that detects an error condition
in relation to a stanza MUST return to the sending entity a stanza
of the same kind (message, presence, or IQ) whose 'type' attribute
is set to a value of "error" (such a stanza is called an "error
stanza" herein).
o The entity that generates an error stanza SHOULD (but is NOT
REQUIRED to) include the original XML sent so that the sender can
inspect and if necessary correct the XML before attempting to
resend.
o An error stanza MUST contain an <error/> child element.
o An <error/> child MUST NOT be included if the 'type' attribute has
a value other than "error" (or if there is no 'type' attribute).
o An entity that receives an error stanza MUST NOT respond to the
stanza with a further error stanza; this helps to prevent looping.
9.3.2 Syntax
The syntax for stanza-related errors is as follows:
<stanza-name to='sender' type='error'>
[RECOMMENDED to include sender XML here]
<error type='error-type'>
<defined-condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<text xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
OPTIONAL descriptive text
</text>
[OPTIONAL application-specific condition element]
</error>
</stanza-name>
The stanza-name is one of message, presence, or iq.
The value of the <error/> element's 'type' attribute MUST be one of
the following:
o cancel -- do not retry (the error is unrecoverable)
o continue -- proceed (the condition was only a warning)
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o modify -- retry after changing the data sent
o auth -- retry after providing credentials
o wait -- retry after waiting (the error is temporary)
The <error/> element:
o MUST contain a child element corresponding to one of the defined
stanza error conditions specified below; this element MUST be
qualified by the 'urn:ietf:params:xml:ns:xmpp-stanzas' namespace.
o MAY contain a <text/> child containing CDATA that describes the
error in more detail; this element MUST be qualified by the
'urn:ietf:params:xml:ns:xmpp-stanzas' namespace and SHOULD possess
an 'xml:lang' attribute.
o MAY contain a child element for an application-specific error
condition; this element MUST be qualified by an
application-defined namespace, and its structure is defined by
that namespace.
The <text/> element is OPTIONAL. If included, it SHOULD be used only
to provide descriptive or diagnostic information that supplements the
meaning of a defined condition or application-specific condition. It
SHOULD NOT be interpreted programmatically by an application. It
SHOULD NOT be used as the error message presented to a user, but MAY
be shown in addition to the error message associated with the
included condition element (or elements).
Finally, to maintain backward compatibility, the schema (specified in
[XMPP-IM]) allows the optional inclusion of a 'code' attribute on the
<error/> element.
9.3.3 Defined Conditions
The following stanza-related error conditions are defined for use in
stanza errors.
o <bad-request/> -- the sender has sent XML that is malformed or
that cannot be processed (e.g., an IQ stanza that includes an
unrecognized value of the 'type' attribute); the associated error
type SHOULD be "modify".
o <conflict/> -- access cannot be granted because an existing
resource or session exists with the same name or address; the
associated error type SHOULD be "cancel".
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o <feature-not-implemented/> -- the feature requested is not
implemented by the recipient or server and therefore cannot be
processed; the associated error type SHOULD be "cancel".
o <forbidden/> -- the requesting entity does not possess the
required permissions to perform the action; the associated error
type SHOULD be "auth".
o <gone/> -- the recipient or server can no longer be contacted at
this address (the error stanza MAY contain a new address in the
CDATA of the <gone/> element); the associated error type SHOULD be
"modify".
o <internal-server-error/> -- the server could not process the
stanza because of a misconfiguration or an otherwise-undefined
internal server error; the associated error type SHOULD be "wait".
o <item-not-found/> -- the addressed JID or item requested cannot be
found; the associated error type SHOULD be "cancel".
o <jid-malformed/> -- the value of the 'to' attribute in the
sender's stanza does not adhere to the syntax defined in
Addressing Scheme (Section 3); the associated error type SHOULD be
"modify".
o <not-acceptable/> -- the recipient or server understands the
request but is refusing to process it because it does not meet
criteria defined by the recipient or server (e.g., a local policy
regarding acceptable words in messages); the associated error type
SHOULD be "modify".
o <not-allowed/> -- the recipient or server does not allow any
entity to perform the action; the associated error type SHOULD be
"cancel".
o <not-authorized/> -- the sender must provide proper credentials
before being allowed to perform the action, or has provided
improper credentials; the associated error type SHOULD be "auth".
o <payment-required/> -- the requesting entity is not authorized to
access the requested service because payment is required; the
associated error type SHOULD be "auth".
o <recipient-unavailable/> -- the intended recipient is temporarily
unavailable; the associated error type SHOULD be "wait" (note: an
application MUST NOT return this error if doing so would provide
information about the intended recipient's network availability to
an entity that is not authorized to know such information).
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o <redirect/> -- the recipient or server is redirecting requests for
this information to another entity, usually temporarily (the error
stanza SHOULD contain the alternate address, which MUST be a valid
JID, in the CDATA of the <redirect/> element); the associated
error type SHOULD be "modify".
o <registration-required/> -- the requesting entity is not
authorized to access the requested service because registration is
required; the associated error type SHOULD be "auth".
o <remote-server-not-found/> -- a remote server or service specified
as part or all of the JID of the intended recipient does not
exist; the associated error type SHOULD be "cancel".
o <remote-server-timeout/> -- a remote server or service specified
as part or all of the JID of the intended recipient could not be
contacted within a reasonable amount of time; the associated error
type SHOULD be "wait".
o <resource-constraint/> -- the server or recipient lacks the system
resources necessary to service the request; the associated error
type SHOULD be "wait".
o <service-unavailable/> -- the server or recipient does not
currently provide the requested service; the associated error type
SHOULD be "cancel".
o <subscription-required/> -- the requesting entity is not
authorized to access the requested service because a subscription
is required; the associated error type SHOULD be "auth".
o <undefined-condition/> -- the error condition is not one of those
defined by the other conditions in this list; any error type may
be associated with this condition, and it SHOULD be used only in
conjunction with an application-specific condition.
o <unexpected-request/> -- the recipient or server understood the
request but was not expecting it at this time (e.g., the request
was out of order); the associated error type SHOULD be "wait".
9.3.4 Application-Specific Conditions
As noted, an application MAY provide application-specific stanza
error information by including a properly-namespaced child in the
error element. The application-specific element SHOULD supplement or
further qualify a defined element. Thus the <error/> element will
contain two or three child elements:
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<iq type='error' id='some-id'>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<too-many-parameters xmlns='application-ns'/>
</error>
</iq>
<message type='error' id='another-id'>
<error type='modify'>
<undefined-condition
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<text xml:lang='en'
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
Some special application diagnostic information...
</text>
<special-application-condition xmlns='application-ns'/>
</error>
</message>
10. Server Rules for Handling XML Stanzas
Compliant server implementations MUST ensure in-order processing of
XML stanzas between any two entities.
Beyond the requirement for in-order processing, each server
implementation will contain its own "delivery tree" for handling
stanzas it receives. Such a tree determines whether a stanza needs
to be routed to another domain, processed internally, or delivered to
a resource associated with a connected node. The following rules
apply:
10.1 No 'to' Address
If the stanza possesses no 'to' attribute, the server SHOULD process
it on behalf of the entity that sent it. Because all stanzas
received from other servers MUST possess a 'to' attribute, this rule
applies only to stanzas received from a registered entity (such as a
client) that is connected to the server. If the server receives a
presence stanza with no 'to' attribute, the server SHOULD broadcast
it to the entities that are subscribed to the sending entity's
presence, if applicable (the semantics of presence broadcast for
instant messaging and presence applications are defined in
[XMPP-IM]). If the server receives an IQ stanza of type "get" or
"set" with no 'to' attribute and it understands the namespace that
qualifies the content of the stanza, it MUST either process the
stanza on behalf of sending entity (where the meaning of "process" is
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determined by the semantics of the qualifying namespace) or return an
error to the sending entity.
10.2 Foreign Domain
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute does not match one of the configured hostnames
of the server itself or a subdomain thereof, the server SHOULD route
the stanza to the foreign domain (subject to local service
provisioning and security policies regarding inter-domain
communication). There are two possible cases:
A server-to-server stream already exists between the two domains: The
sender's server routes the stanza to the authoritative server for
the foreign domain over the existing stream
There exists no server-to-server stream between the two domains: The
sender's server (1) resolves the hostname of the foreign domain
(as defined under Server-to-Server Communications (Section 14.4)),
(2) negotiates a server-to-server stream between the two domains
(as defined under Use of TLS (Section 5) and Use of SASL (Section
6)), and (3) routes the stanza to the authoritative server for the
foreign domain over the newly-established stream
If routing to the recipient's server is unsuccessful, the sender's
server MUST return an error to the sender; if the recipient's server
can be contacted but delivery by the recipient's server to the
recipient is unsuccessful, the recipient's server MUST return an
error to the sender by way of the sender's server.
10.3 Subdomain
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute matches a subdomain of one of the configured
hostnames of the server itself, the server MUST either process the
stanza itself or route the stanza to a specialized service that is
responsible for that subdomain (if the subdomain is configured), or
return an error to the sender (if the subdomain is not configured).
10.4 Mere Domain or Specific Resource
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute matches a configured hostname of the server
itself and the JID contained in the 'to' attribute is of the form
<domain> or <domain/resource>, the server (or a defined resource
thereof) MUST either process the stanza as appropriate for the stanza
kind or return an error stanza to the sender.
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10.5 Node in Same Domain
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute matches a configured hostname of the server
itself and the JID contained in the 'to' attribute is of the form
<node@domain> or <node@domain/resource>, the server SHOULD deliver
the stanza to the intended recipient of the stanza as represented by
the JID contained in the 'to' attribute. The following rules apply:
1. If the JID contains a resource identifier (i.e., is of the form
<node@domain/resource>) and there exists a connected resource
that matches the full JID, the recipient's server SHOULD deliver
the stanza to the stream or session that exactly matches the
resource identifier.
2. If the JID contains a resource identifier and there exists no
connected resource that matches the full JID, the recipient's
server SHOULD return a <service-unavailable/> stanza error to the
sender.
3. If the JID is of the form <node@domain> and there exists at least
one connected resource for the node, the recipient's server MUST
deliver the stanza to at least one of the connected resources,
according to application-specific rules (a set of delivery rules
for instant messaging and presence applications is defined in
[XMPP-IM]).
11. XML Usage within XMPP
11.1 Restrictions
XMPP is a simplified and specialized protocol for streaming XML
elements in order to exchange structured information in close to real
time. Because XMPP does not require the parsing of arbitrary and
complete XML documents, there is no requirement that XMPP needs to
support the full feature set of [XML]. In particular, the following
restrictions apply.
With regard to XML generation, an XMPP implementation MUST NOT inject
into an XML stream any of the following:
o comments (as defined in Section 2.5 of [XML])
o processing instructions (Section 2.6 therein)
o internal or external DTD subsets (Section 2.8 therein)
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o internal or external entity references (Section 4.2 therein) with
the exception of predefined entities (Section 4.6 therein)
o character data or attribute values containing unescaped characters
that map to the predefined entities (Section 4.6 therein); such
characters MUST be escaped
With regard to XML processing, if an XMPP implementation receives
such restricted XML data, it MUST ignore the data.
11.2 XML Namespace Names and Prefixes
XML Namespaces [XML-NAMES] are used within all XMPP-compliant XML to
create strict boundaries of data ownership. The basic function of
namespaces is to separate different vocabularies of XML elements that
are structurally mixed together. Ensuring that XMPP-compliant XML is
namespace-aware enables any allowable XML to be structurally mixed
with any data element within XMPP. Rules for XML namespace names and
prefixes are defined in the following subsections.
11.2.1 Streams Namespace
A streams namespace declaration is REQUIRED in all XML stream
headers. The name of the streams namespace MUST be 'http://
etherx.jabber.org/streams'. The element names of the <stream/>
element and its <features/> and <error/> children MUST be qualified
by the streams namespace prefix in all instances. An implementation
SHOULD generate only the 'stream:' prefix for these elements, and for
historical reasons MAY accept only the 'stream:' prefix.
11.2.2 Default Namespace
A default namespace declaration is REQUIRED and is used in all XML
streams in order to define the allowable first-level children of the
root stream element. This namespace declaration MUST be the same for
the initial stream and the response stream so that both streams are
qualified consistently. The default namespace declaration applies to
the stream and all stanzas sent within a stream (unless explicitly
qualified by another namespace, or by the prefix of the streams
namespace or the dialback namespace).
A server implementation MUST support the following two default
namespaces (for historical reasons, some implementations MAY support
only these two default namespaces):
o jabber:client -- this default namespace is declared when the
stream is used for communications between a client and a server
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o jabber:server -- this default namespace is declared when the
stream is used for communications between two servers
A client implementation MUST support the 'jabber:client' default
namespace, and for historical reasons MAY support only that default
namespace.
An implementation MUST NOT generate namespace prefixes for elements
in the default namespace if the default namespace is 'jabber:client'
or 'jabber:server'. An implementation SHOULD NOT generate namespace
prefixes for elements qualified by content (as opposed to stream)
namespaces other than 'jabber:client' and 'jabber:server'.
Note: The 'jabber:client' and 'jabber:server' namespaces are nearly
identical but are used in different contexts (client-to-server
communications for 'jabber:client' and server-to-server
communications for 'jabber:server'). The only difference between the
two is that the 'to' and 'from' attributes are OPTIONAL on stanzas
sent within 'jabber:client', whereas they are REQUIRED on stanzas
sent within 'jabber:server'. If a compliant implementation accepts a
stream that is qualified by the 'jabber:client' or 'jabber:server'
namespace, it MUST support the common attributes (Section 9.1) and
basic semantics (Section 9.2) of all three core stanza kinds
(message, presence, and IQ).
11.2.3 Dialback Namespace
A dialback namespace declaration is REQUIRED for all elements used in
server dialback (Section 8). The name of the dialback namespace MUST
be 'jabber:server:dialback'. All elements qualified by this
namespace MUST be prefixed. An implementation SHOULD generate only
the 'db:' prefix for such elements and MAY accept only the 'db:'
prefix.
11.3 Validation
Except as noted with regard to 'to' and 'from' addresses for stanzas
within the 'jabber:server' namespace, a server is not responsible for
validating the XML elements forwarded to a client or another server;
an implementation MAY choose to provide only validated data elements
but is NOT REQUIRED to do so (although an implementation MUST NOT
accept XML that is not well-formed). Clients SHOULD NOT rely on the
ability to send data which does not conform to the schemas, and
SHOULD ignore any non-conformant elements or attributes on the
incoming XML stream. Validation of XML streams and stanzas is NOT
REQUIRED or recommended, and schemas are included herein for
descriptive purposes only.
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11.4 Inclusion of Text Declaration
Implementations SHOULD send a text declaration before sending a
stream header. Applications MUST follow the rules in [XML] regarding
the circumstances under which a text declaration is included.
11.5 Character Encoding
Implementations MUST support the UTF-8 (RFC 3269 [UTF-8])
transformation of Universal Character Set (ISO/IEC 10646-1 [UCS2])
characters, as required by RFC 2277 [CHARSET]. Implementations MUST
NOT attempt to use any other encoding.
12. Core Compliance Requirements
This section summarizes the specific aspects of the Extensible
Messaging and Presence Protocol that MUST be supported by servers and
clients in order to be considered compliant implementations, as well
as additional protocol aspects that SHOULD be supported. For
compliance purposes, we draw a distinction between core protocols
(which MUST be supported by any server or client, regardless of the
specific application) and instant messaging protocols (which MUST be
supported only by instant messaging and presence applications built
on top of the core protocols). Compliance requirements that apply to
all servers and clients are specified in this section; compliance
requirements for instant messaging servers and clients are specified
in the corresponding section of [XMPP-IM].
12.1 Servers
In addition to all defined requirements with regard to security, XML
usage, and internationalization, a server MUST support the following
core protocols in order to be considered compliant:
o Application of the [NAMEPREP], Nodeprep (Appendix A), and
Resourceprep (Appendix B) profiles of [STRINGPREP] to addresses
(including ensuring that domain identifiers are internationalized
domain names as defined in [IDNA])
o XML streams (Section 4), including Use of TLS (Section 5), Use of
SASL (Section 6), and Resource Binding (Section 7)
o The basic semantics of the three defined stanza kinds (i.e.,
<message/>, <presence/>, and <iq/>) as specified in stanza
semantics (Section 9.2)
o Generation (and, where appropriate, handling) of error syntax and
semantics related to streams, TLS, SASL, and XML stanzas
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In addition, a server SHOULD support the following core protocol:
o Server dialback (Section 8)
12.2 Clients
A client MUST support the following core protocols in order to be
considered compliant:
o XML streams (Section 4), including Use of TLS (Section 5), Use of
SASL (Section 6), and Resource Binding (Section 7)
o The basic semantics of the three defined stanza kinds (i.e.,
<message/>, <presence/>, and <iq/>) as specified in stanza
semantics (Section 9.2)
o Handling (and, where appropriate, generation) of error syntax and
semantics related to streams, TLS, SASL, and XML stanzas
In addition, a client SHOULD support the following core protocols:
o Generation of addresses to which the [NAMEPREP], Nodeprep
(Appendix A), and Resourceprep (Appendix B) profiles of
[STRINGPREP] can be applied without failing
13. Internationalization Considerations
XML streams MUST be encoded in UTF-8 as specified under Character
Encoding (Section 11.5). As specified under Stream Attributes
(Section 4.2), an XML stream SHOULD include an 'xml:lang' attribute
that is treated as the default language for any XML character data
sent over the stream that is intended to be presented to a human
user. As specified under xml:lang (Section 9.1.5), an XML stanza
SHOULD include an 'xml:lang' attribute if the stanza contains XML
character data that is intended to be presented to a human user. A
server SHOULD apply the default 'xml:lang' attribute to stanzas it
routes or delivers on behalf of connected entities, and MUST NOT
modify or delete 'xml:lang' attributes from stanzas it receives from
other entities.
14. Security Considerations
14.1 High Security
For the purposes of XMPP communications (client-to-server and
server-to-server), the term "high security" refers to the use of
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security technologies that provide both mutual authentication and
integrity-checking; in particular, when using certificate-based
authentication to provide high security, a chain-of-trust SHOULD be
established out-of-band, although a shared certificate authority
signing certificates could allow a previously unknown certificate to
establish trust in-band. See Section 14.2 below regarding certificate
validation procedures.
Implementations MUST support high security. Service provisioning
SHOULD use high security, subject to local security policies.
14.2 Certificate Validation
When an XMPP peer communicates with another peer securely, it MUST
validate the peer's certificate. There are three possible cases:
Case #1: The peer contains an End Entity certificate which appears to
be certified by a chain of certificates terminating in a trust
anchor (as described in Section 6.1 of [X509]).
Case #2: The peer certificate is certified by a Certificate Authority
not known to the validating peer.
Case #3: The peer certificate is self-signed.
In Case #1, the validating peer MUST do one of two things:
1. Verify the peer certificate according to the rules of [X509].
The certificate SHOULD then be checked against the expected
identity of the peer following the rules described in [HTTP-TLS],
except that a subjectAltName extension of type "xmpp" MUST be
used as the identity if present. If one of these checks fails,
user-oriented clients MUST either notify the user (clients MAY
give the user the opportunity to continue with the connection in
any case) or terminate the connection with a bad certificate
error. Automated clients SHOULD terminate the connection (with a
bad certificate error) and log the error to an appropriate audit
log. Automated clients MAY provide a configuration setting that
disables this check, but MUST provide a setting which enables it.
2. The peer SHOULD show the certificate to a user for approval,
including the entire certificate chain. The peer MUST Cache the
certificate (or some non-forgeable representation such as a
hash). In future connections, the peer MUST verify that the same
certificate was presented and MUST notify the user if it has
changed.
In Case #2 and Case #3, implementations SHOULD act as in (2) above.
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14.3 Client-to-Server Communications
A compliant implementation MUST support both TLS and SASL for
connections to a server.
The TLS protocol for encrypting XML streams (defined under Use of TLS
(Section 5)) provides a reliable mechanism for helping to ensure the
confidentiality and data integrity of data exchanged between two
entities.
The SASL protocol for authenticating XML streams (defined under Use
of SASL (Section 6)) provides a reliable mechanism for validating
that a client connecting to a server is who it claims to be.
Client-to-server communications MUST NOT proceed until the DNS
hostname asserted by the server has been resolved. Such resolutions
SHOULD first attempt to resolve the hostname using an [SRV] Service
of "xmpp-client" and Proto of "tcp", resulting in resource records
such as "_xmpp-client._tcp.example.com." (the use of the string
"xmpp-client" for the service identifier is consistent with the IANA
registration). If the SRV lookup fails, the fallback is a normal
IPv4/IPv6 address record resolution to determine the IP address,
using the "xmpp-client" port of 5222 registered with the IANA.
The IP address and method of access of clients MUST NOT be made
public by a server, nor are any connections other than the original
server connection required. This helps to protect the client's
server from direct attack or identification by third parties.
14.4 Server-to-Server Communications
A compliant implementation MUST support both TLS and SASL for
inter-domain communications. For historical reasons, a compliant
implementation SHOULD also support Server Dialback (Section 8).
Because service provisioning is a matter of policy, it is OPTIONAL
for any given domain to communicate with other domains, and
server-to-server communications MAY be disabled by the administrator
of any given deployment. If a particular domain enables inter-domain
communications, it SHOULD enable high security.
Administrators may want to require use of SASL for server-to-server
communications in order to ensure both authentication and
confidentiality (e.g., on an organization's private network).
Compliant implementations SHOULD support SASL for this purpose.
Inter-domain connections MUST NOT proceed until the DNS hostnames
asserted by the servers have been resolved. Such resolutions MUST
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first attempt to resolve the hostname using an [SRV] Service of
"xmpp-server" and Proto of "tcp", resulting in resource records such
as "_xmpp-server._tcp.example.com." (the use of the string
"xmpp-server" for the service identifier is consistent with the IANA
registration; note well that the "xmpp-server" service identifier
supersedes the earlier use of a "jabber" service identifier, since
the earlier usage did not conform to [SRV]; implementations desiring
to be backward compatible should continue to look for or answer to
the "jabber" service identifier as well). If the SRV lookup fails,
the fallback is a normal IPv4/IPv6 address record resolution to
determine the IP address, using the "xmpp-server" port of 5269
registered with the IANA.
Server dialback helps protect against domain spoofing, thus making it
more difficult to spoof XML stanzas. It is not a mechanism for
authenticating, securing, or encrypting streams between servers as is
done via SASL and TLS. Furthermore, it is susceptible to DNS
poisoning attacks unless DNSSec [DNSSEC] is used, and even if the DNS
information is accurate, dialback cannot protect from attacks where
the attacker is capable of hijacking the IP address of the remote
domain. Domains requiring robust security SHOULD use TLS and SASL.
If SASL is used for server-to-server authentication, dialback SHOULD
NOT be used since it is unnecessary.
14.5 Order of Layers
The order of layers in which protocols MUST be stacked is as follows:
1. TCP
2. TLS
3. SASL
4. XMPP
The rationale for this order is that [TCP] is the base connection
layer used by all of the protocols stacked on top of TCP, [TLS] is
often provided at the operating system layer, [SASL] is often
provided at the application layer, and XMPP is the application
itself.
14.6 Lack of SASL Channel Binding to TLS
The SASL framework does not provide a mechanism to bind SASL
authentication to a security layer providing confidentiality and
integrity protection that was negotiated at a lower layer. This lack
of a "channel binding" prevents SASL from being able to verify that
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the source and destination end points to which the lower layer's
security is bound are equivalent to the end points that SASL is
authenticating. If the end points are not identical, the lower
layer's security cannot be trusted to protect data transmitted
between the SASL authenticated entities. In such a situation, a SASL
security layer should be negotiated which effectively ignores the
presence of the lower layer security.
14.7 Mandatory-to-Implement Technologies
At a minimum, all implementations MUST support the following
mechanisms:
for authentication: the SASL [DIGEST-MD5] mechanism
for confidentiality: TLS (using the TLS_RSA_WITH_3DES_EDE_CBC_SHA
cipher)
for both: TLS plus SASL EXTERNAL(using the
TLS_RSA_WITH_3DES_EDE_CBC_SHA cipher supporting client-side
certificates)
14.8 Firewalls
Communications using XMPP normally occur over [TCP] sockets on port
5222 (client-to-server) or port 5269 (server-to-server), as
registered with the IANA (see IANA Considerations (Section 15)). Use
of these well-known ports allows administrators to easily enable or
disable XMPP activity through existing and commonly-deployed
firewalls.
14.9 Use of base64 in SASL
Both the client and the server MUST verify any [BASE64] data received
during SASL negotiation. An implementation MUST reject (not ignore)
any characters that are not explicitly allowed by the base64
alphabet; this helps to guard against creation of a covert channel
that could be used to "leak" information. An implementation MUST NOT
break on invalid input and MUST reject any sequence of base64
characters containing the pad ('=') character if that character is
included as something other than the last character of the data (e.g.
"=AAA" or "BBBB=CCC"); this helps to guard against buffer overflow
attacks and other attacks on the implementation. Base encoding
visually hides otherwise easily recognized information, such as
passwords, but does not provide any computational confidentiality.
Base 64 encoding MUST follow the definition in Section 3 of RFC 3548
[BASE64].
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14.10 Stringprep Profiles
XMPP makes use of the [NAMEPREP] profile of [STRINGPREP] for
processing of domain identifiers; for security considerations related
to Nameprep, refer to the appropriate section of [NAMEPREP].
In addition, XMPP defines two profiles of [STRINGPREP]: Nodeprep
(Appendix A) for node identifiers and Resourceprep (Appendix B) for
resource identifiers.
The Unicode and ISO/IEC 10646 repertoires have many characters that
look similar. In many cases, users of security protocols might do
visual matching, such as when comparing the names of trusted third
parties. Because it is impossible to map similar-looking characters
without a great deal of context such as knowing the fonts used,
stringprep does nothing to map similar-looking characters together
nor to prohibit some characters because they look like others.
A node identifier can be employed as one part of an entity's address
in XMPP. One common usage is as the username of an instant messaging
user; another is as the name of a multi-user chat room; and many
other kinds of entities could use node identifiers as part of their
addresses. The security of such services could be compromised based
on different interpretations of the internationalized node
identifier; for example, a user entering a single internationalized
node identifier could access another user's account information, or a
user could gain access to an otherwise restricted chat room or
service.
A resource identifier can be employed as one part of an entity's
address in XMPP. One common usage is as the name for an instant
messaging user's connected resource (active session); another is as
the nickname of a user in a multi-user chat room; and many other
kinds of entities could use resource identifiers as part of their
addresses. The security of such services could be compromised based
on different interpretations of the internationalized resource
identifier; for example, a user could attempt to initiate multiple
sessions with the same name, or a user could send a message to
someone other than the intended recipient in a multi-user chat room.
15. IANA Considerations
15.1 XML Namespace Name for TLS Data
A URN sub-namespace for TLS-related data in the Extensible Messaging
and Presence Protocol (XMPP) is defined as follows. (This namespace
name adheres to the format defined in The IETF XML Registry
[XML-REG].)
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URI: urn:ietf:params:xml:ns:xmpp-tls
Specification: XXXX
Description: This is the XML namespace name for TLS-related data in
the Extensible Messaging and Presence Protocol (XMPP) as defined
by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
15.2 XML Namespace Name for SASL Data
A URN sub-namespace for SASL-related data in the Extensible Messaging
and Presence Protocol (XMPP) is defined as follows. (This namespace
name adheres to the format defined in [XML-REG].)
URI: urn:ietf:params:xml:ns:xmpp-sasl
Specification: XXXX
Description: This is the XML namespace name for SASL-related data in
the Extensible Messaging and Presence Protocol (XMPP) as defined
by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
15.3 XML Namespace Name for Stream Errors
A URN sub-namespace for stream-related error data in the Extensible
Messaging and Presence Protocol (XMPP) is defined as follows. (This
namespace name adheres to the format defined in [XML-REG].)
URI: urn:ietf:params:xml:ns:xmpp-streams
Specification: XXXX
Description: This is the XML namespace name for stream-related error
data in the Extensible Messaging and Presence Protocol (XMPP) as
defined by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
15.4 XML Namespace Name for Resource Binding
A URN sub-namespace for resource binding in the Extensible Messaging
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and Presence Protocol (XMPP) is defined as follows. (This namespace
name adheres to the format defined in [XML-REG].)
URI: urn:ietf:params:xml:ns:xmpp-bind
Specification: XXXX
Description: This is the XML namespace name for resource binding in
the Extensible Messaging and Presence Protocol (XMPP) as defined
by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
15.5 XML Namespace Name for Stanza Errors
A URN sub-namespace for stanza-related error data in the Extensible
Messaging and Presence Protocol (XMPP) is defined as follows. (This
namespace name adheres to the format defined in [XML-REG].)
URI: urn:ietf:params:xml:ns:xmpp-stanzas
Specification: XXXX
Description: This is the XML namespace name for stanza-related error
data in the Extensible Messaging and Presence Protocol (XMPP) as
defined by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
15.6 Nodeprep Profile of Stringprep
The Nodeprep profile of stringprep is defined under Nodeprep
(Appendix A). The IANA registers Nodeprep in the stringprep profile
registry.
Name of this profile:
Nodeprep
RFC in which the profile is defined:
XXXX
Indicator whether or not this is the newest version of the profile:
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This is the first version of Nodeprep
15.7 Resourceprep Profile of Stringprep
The Resourceprep profile of stringprep is defined under Resourceprep
(Appendix B). The IANA registers Resourceprep in the stringprep
profile registry.
Name of this profile:
Resourceprep
RFC in which the profile is defined:
XXXX
Indicator whether or not this is the newest version of the profile:
This is the first version of Resourceprep
15.8 GSSAPI Service Name
The IANA registers "xmpp" as a GSSAPI [GSS-API] service name, as
defined under SASL Definition (Section 6.3).
15.9 Port Numbers
The IANA currently registers "jabber-client" and "jabber-server" as
keywords for [TCP] ports 5222 and 5269 respectively. The IANA shall
change these registrations to "xmpp-client" and "xmpp-server"
respectively.
These ports SHOULD be used for client-to-server and server-to-server
communications respectively, but their use is NOT REQUIRED.
Normative References
[ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 3548, July 2003.
[CHARSET] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998.
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[DIGEST-MD5]
Leach, P. and C. Newman, "Using Digest Authentication as a
SASL Mechanism", RFC 2831, May 2000.
[DNS] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[GSS-API] Linn, J., "Generic Security Service Application Program
Interface, Version 2", RFC 2078, January 1997.
[HTTP-TLS]
Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[IMP-REQS]
Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging /
Presence Protocol Requirements", RFC 2779, February 2000.
[IPv6] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[LANGTAGS]
Alvestrand, H., "Tags for the Identification of
Languages", BCP 47, RFC 3066, January 2001.
[IDNA] Faltstrom, P., Hoffman, P. and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003.
[NAMEPREP]
Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
Profile for Internationalized Domain Names (IDN)", RFC
3491, March 2003.
[SASL] Myers, J., "Simple Authentication and Security Layer
(SASL)", RFC 2222, October 1997.
[SRV] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[STRINGPREP]
Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings ("STRINGPREP")", RFC 3454,
December 2002.
[TCP] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981.
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[TERMS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[TLS] Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A.
and P. Kocher, "The TLS Protocol Version 1.0", RFC 2246,
January 1999.
[UCS2] International Organization for Standardization,
"Information Technology - Universal Multiple-octet coded
Character Set (UCS) - Amendment 2: UCS Transformation
Format 8 (UTF-8)", ISO Standard 10646-1 Addendum 2,
October 1996.
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[X509] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
"Extensible Markup Language (XML) 1.0 (2nd ed)", W3C
REC-xml, October 2000, <http://www.w3.org/TR/REC-xml>.
[XML-NAMES]
Bray, T., Hollander, D. and A. Layman, "Namespaces in
XML", W3C REC-xml-names, January 1999, <http://www.w3.org/
TR/REC-xml-names>.
Informative References
[ACAP] Newman, C. and J. Myers, "ACAP -- Application
Configuration Access Protocol", RFC 2244, November 1997.
[DNSSEC] Eastlake, D., "Domain Name System Security Extensions",
RFC 2535, March 1999.
[HTTP] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[IMAP] Crispin, M., "Internet Message Access Protocol - Version
4rev1", RFC 2060, December 1996.
[JSF] Jabber Software Foundation, "Jabber Software Foundation",
<http://www.jabber.org/>.
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[POP3] Myers, J. and M. Rose, "Post Office Protocol - Version 3",
STD 53, RFC 1939, May 1996.
[URI] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[USINGTLS]
Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC
2595, June 1999.
[XML-REG] Mealling, M., "The IETF XML Registry",
draft-mealling-iana-xmlns-registry-05 (work in progress),
June 2003.
[XMPP-IM] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
draft-ietf-xmpp-im-19 (work in progress), November 2003.
Author's Address
Peter Saint-Andre
Jabber Software Foundation
EMail: stpeter@jabber.org
Appendix A. Nodeprep
A.1 Introduction
This appendix defines the "Nodeprep" profile of [STRINGPREP]. As
such, it specifies processing rules that will enable users to enter
internationalized node identifiers in the Extensible Messaging and
Presence Protocol (XMPP) and have the highest chance of getting the
content of the strings correct. (An XMPP node identifier is the
optional portion of an XMPP address that precedes a domain identifier
and the '@' separator; it is often but not exclusively associated
with an instant messaging username.) These processing rules are
intended only for XMPP node identifiers and are not intended for
arbitrary text or any other aspect of an XMPP address.
This profile defines the following, as required by [STRINGPREP]:
o The intended applicability of the profile: internationalized node
identifiers within XMPP
o The character repertoire that is the input and output to
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stringprep: Unicode 3.2, specified in Section 2 of this Appendix
o The mappings used: specified in Section 3
o The Unicode normalization used: specified in Section 4
o The characters that are prohibited as output: specified in Section
5
o Bidirectional character handling: specified in Section 6
A.2 Character Repertoire
This profile uses Unicode 3.2 with the list of unassigned code points
being Table A.1, both defined in Appendix A of [STRINGPREP].
A.3 Mapping
This profile specifies mapping using the following tables from
[STRINGPREP]:
Table B.1
Table B.2
A.4 Normalization
This profile specifies using Unicode normalization form KC, as
described in [STRINGPREP].
A.5 Prohibited Output
This profile specifies prohibiting use of the following tables from
[STRINGPREP].
Table C.1.1
Table C.1.2
Table C.2.1
Table C.2.2
Table C.3
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Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
In addition, the following Unicode characters are also prohibited:
#x22 (")
#x26 (&)
#x27 (')
#x2F (/)
#x3A (:)
#x3C (<)
#x3E (>)
#x40 (@)
A.6 Bidirectional Characters
This profile specifies checking bidirectional strings as described in
Section 6 of [STRINGPREP].
Appendix B. Resourceprep
B.1 Introduction
This appendix defines the "Resourceprep" profile of [STRINGPREP]. As
such, it specifies processing rules that will enable users to enter
internationalized resource identifiers in the Extensible Messaging
and Presence Protocol (XMPP) and have the highest chance of getting
the content of the strings correct. (An XMPP resource identifier is
the optional portion of an XMPP address that follows a domain
identifier and the '/' separator; it is often but not exclusively
associated with an instant messaging session name.) These processing
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rules are intended only for XMPP resource identifiers and are not
intended for arbitrary text or any other aspect of an XMPP address.
This profile defines the following, as required by [STRINGPREP]:
o The intended applicability of the profile: internationalized
resource identifiers within XMPP
o The character repertoire that is the input and output to
stringprep: Unicode 3.2, specified in Section 2 of this Appendix
o The mappings used: specified in Section 3
o The Unicode normalization used: specified in Section 4
o The characters that are prohibited as output: specified in Section
5
o Bidirectional character handling: specified in Section 6
B.2 Character Repertoire
This profile uses Unicode 3.2 with the list of unassigned code points
being Table A.1, both defined in Appendix A of [STRINGPREP].
B.3 Mapping
This profile specifies mapping using the following tables from
[STRINGPREP]:
Table B.1
B.4 Normalization
This profile specifies using Unicode normalization form KC, as
described in [STRINGPREP].
B.5 Prohibited Output
This profile specifies prohibiting use of the following tables from
[STRINGPREP].
Table C.1.2
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Table C.2.1
Table C.2.2
Table C.3
Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
B.6 Bidirectional Characters
This profile specifies checking bidirectional strings as described in
Section 6 of [STRINGPREP].
Appendix C. XML Schemas
The following XML schemas are descriptive, not normative. For
schemas defining the 'jabber:client' and 'jabber:server' namespaces,
refer to [XMPP-IM].
C.1 Streams namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='http://etherx.jabber.org/streams'
xmlns='http://etherx.jabber.org/streams'
elementFormDefault='unqualified'>
<xs:import namespace='http://www.w3.org/XML/1998/namespace'
schemaLocation='http://www.w3.org/2001/xml.xsd'/>
<xs:element name='stream'>
<xs:complexType>
<xs:sequence>
<xs:element ref='features' minOccurs='0' maxOccurs='1'/>
<xs:choice minOccurs='0' maxOccurs='1'>
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<xs:any namespace='jabber:client'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:any namespace='jabber:server'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:choice>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='from' type='xs:string' use='optional'/>
<xs:attribute name='id' type='xs:NMTOKEN' use='optional'/>
<xs:attribute name='to' type='xs:string' use='optional'/>
<xs:attribute name='version' type='xs:decimal' use='optional'/>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='features'>
<xs:complexType>
<xs:choice minOccurs='0' maxOccurs='unbounded'>
<xs:any namespace='urn:ietf:params:xml:ns:xmpp-tls'/>
<xs:any namespace='urn:ietf:params:xml:ns:xmpp-sasl'/>
<xs:any namespace='urn:ietf:params:xml:ns:xmpp-bind'/>
<xs:any namespace='urn:ietf:params:xml:ns:xmpp-session'/>
<xs:any namespace='##other'/>
</xs:choice>
</xs:complexType>
</xs:element>
<xs:element name='error'>
<xs:complexType>
<xs:sequence>
<xs:any namespace='urn:ietf:params:xml:ns:xmpp-streams'
maxOccurs='2'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
C.2 Stream error namespace
<?xml version='1.0' encoding='UTF-8'?>
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<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
xmlns:xml='http://www.w3.org/XML/1998/namespace'
targetNamespace='urn:ietf:params:xml:ns:xmpp-streams'
xmlns='urn:ietf:params:xml:ns:xmpp-streams'
elementFormDefault='qualified'>
<xs:import namespace='http://www.w3.org/XML/1998/namespace'
schemaLocation='http://www.w3.org/2001/xml.xsd'/>
<xs:element name='bad-format' type='empty'/>
<xs:element name='bad-namespace-prefix' type='empty'/>
<xs:element name='conflict' type='empty'/>
<xs:element name='connection-timeout' type='empty'/>
<xs:element name='host-gone' type='empty'/>
<xs:element name='host-unknown' type='empty'/>
<xs:element name='improper-addressing' type='empty'/>
<xs:element name='internal-server-error' type='empty'/>
<xs:element name='invalid-from' type='empty'/>
<xs:element name='invalid-id' type='empty'/>
<xs:element name='invalid-namespace' type='empty'/>
<xs:element name='invalid-xml' type='empty'/>
<xs:element name='not-authorized' type='empty'/>
<xs:element name='policy-violation' type='empty'/>
<xs:element name='remote-connection-failed' type='empty'/>
<xs:element name='resource-constraint' type='empty'/>
<xs:element name='restricted-xml' type='empty'/>
<xs:element name='see-other-host' type='xs:string'/>
<xs:element name='system-shutdown' type='empty'/>
<xs:element name='undefined-condition' type='empty'/>
<xs:element name='unsupported-encoding' type='empty'/>
<xs:element name='unsupported-stanza-type' type='empty'/>
<xs:element name='unsupported-version' type='empty'/>
<xs:element name='xml-not-well-formed' type='empty'/>
<xs:element name='text' type='xs:string'>
<xs:complexType>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
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C.3 TLS namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-tls'
xmlns='urn:ietf:params:xml:ns:xmpp-tls'
elementFormDefault='qualified'>
<xs:element name='starttls'>
<xs:complexType>
<xs:sequence>
<xs:element
ref='required'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='required' type='empty'/>
<xs:element name='proceed' type='empty'/>
<xs:element name='failure' type='empty'/>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
C.4 SASL namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-sasl'
xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
elementFormDefault='qualified'>
<xs:element name='mechanisms'>
<xs:complexType>
<xs:sequence>
<xs:element ref='mechanism' maxOccurs='unbounded'/>
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</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='mechanism' type='xs:string'/>
<xs:element name='auth'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute name='mechanism'
type='xs:NMTOKEN'
use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='challenge' type='xs:NMTOKEN'/>
<xs:element name='response' type='xs:NMTOKEN'/>
<xs:element name='abort' type='empty'/>
<xs:element name='success' type='empty'/>
<xs:element name='failure'>
<xs:complexType>
<xs:choice maxOccurs='1'>
<xs:element ref='aborted'/>
<xs:element ref='incorrect-encoding'/>
<xs:element ref='invalid-authzid'/>
<xs:element ref='invalid-mechanism'/>
<xs:element ref='mechanism-too-weak'/>
<xs:element ref='not-authorized'/>
<xs:element ref='temporary-auth-failure'/>
</xs:choice>
</xs:complexType>
</xs:element>
<xs:element name='aborted' type='empty'/>
<xs:element name='incorrect-encoding' type='empty'/>
<xs:element name='invalid-authzid' type='empty'/>
<xs:element name='invalid-mechanism' type='empty'/>
<xs:element name='mechanism-too-weak' type='empty'/>
<xs:element name='not-authorized' type='empty'/>
<xs:element name='temporary-auth-failure' type='empty'/>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
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</xs:restriction>
</xs:simpleType>
</xs:schema>
C.5 Resource binding namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-bind'
xmlns='urn:ietf:params:xml:ns:xmpp-bind'
elementFormDefault='qualified'>
<xs:element name='bind'>
<xs:complexType>
<xs:choice minOccurs='0' maxOccurs='1'>
<xs:element ref='resource'/>
<xs:element ref='jid'/>
</xs:choice>
</xs:complexType>
</xs:element>
<xs:element name='resource' type='xs:string'/>
<xs:element name='jid' type='xs:string'/>
</xs:schema>
C.6 Dialback namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:server:dialback'
xmlns='jabber:server:dialback'
elementFormDefault='qualified'>
<xs:element name='result'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'>
<xs:attribute name='from' type='xs:string' use='required'/>
<xs:attribute name='to' type='xs:string' use='required'/>
<xs:attribute name='type' use='optional'>
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<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='invalid'/>
<xs:enumeration value='valid'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='verify'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'>
<xs:attribute name='from' type='xs:string' use='required'/>
<xs:attribute name='id' type='xs:NMTOKEN' use='required'/>
<xs:attribute name='to' type='xs:string' use='required'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='invalid'/>
<xs:enumeration value='valid'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
</xs:schema>
C.7 Stanza error namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
xmlns:xml='http://www.w3.org/XML/1998/namespace'
targetNamespace='urn:ietf:params:xml:ns:xmpp-stanzas'
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'
elementFormDefault='qualified'>
<xs:import namespace='http://www.w3.org/XML/1998/namespace'
schemaLocation='http://www.w3.org/2001/xml.xsd'/>
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<xs:element name='bad-request' type='empty'/>
<xs:element name='conflict' type='empty'/>
<xs:element name='feature-not-implemented' type='empty'/>
<xs:element name='forbidden' type='empty'/>
<xs:element name='gone' type='xs:string'/>
<xs:element name='internal-server-error' type='empty'/>
<xs:element name='item-not-found' type='empty'/>
<xs:element name='jid-malformed' type='empty'/>
<xs:element name='not-acceptable' type='empty'/>
<xs:element name='not-allowed' type='empty'/>
<xs:element name='payment-required' type='empty'/>
<xs:element name='recipient-unavailable' type='empty'/>
<xs:element name='redirect' type='xs:string'/>
<xs:element name='registration-required' type='empty'/>
<xs:element name='remote-server-not-found' type='empty'/>
<xs:element name='remote-server-timeout' type='empty'/>
<xs:element name='resource-constraint' type='empty'/>
<xs:element name='service-unavailable' type='empty'/>
<xs:element name='subscription-required' type='empty'/>
<xs:element name='undefined-condition' type='empty'/>
<xs:element name='unexpected-request' type='empty'/>
<xs:element name='text' type='xs:string'>
<xs:complexType>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
Appendix D. Differences Between Core Jabber Protocol and XMPP
This section is non-normative.
XMPP has been adapted from the protocols originally developed in the
Jabber open-source community, which can be thought of as "XMPP 0.9".
Because there exists a large installed base of Jabber implementations
and deployments, it may be helpful to specify the key differences
between Jabber and XMPP in order to expedite and encourage upgrades
of those implementations and deployments to XMPP. This section
summarizes the core differences, while the corresponding section of
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[XMPP-IM] summarizes the differences that relate specifically to
instant messaging and presence applications.
D.1 Channel Encryption
It is common practice in the Jabber community to use SSL for channel
encryption on ports other than 5222 and 5269 (the convention is to
use ports 5223 and 5270). XMPP uses TLS over the IANA-registered
ports for channel encryption, as defined under Use of TLS (Section 5)
herein.
D.2 Authentication
The client-server authentication protocol developed in the Jabber
community uses a basic IQ interaction qualified by the
'jabber:iq:auth' namespace (documentation of this protocol is
contained in "JEP-0078: Non-SASL Authentication", published by the
Jabber Software Foundation [JSF]). XMPP uses SASL for
authentication, as defined under Use of SASL (Section 6) herein.
The Jabber community does not currently possess an authentication
protocol for server-to-server communications, only the Server
Dialback (Section 8) protocol to prevent server spoofing. XMPP
augments Server Dialback with a true server-to-server authentication
protocol, as defined under Use of SASL (Section 6) herein.
D.3 Resource Binding
Resource binding in the Jabber community is handled via the
'jabber:iq:auth' namespace that is also used for client
authentication with a server. XMPP defines a dedicated namespace for
resource binding as well as the ability for a server to generate a
resource identifier on behalf of a client, as defined under Resource
Binding (Section 7).
D.4 JID Processing
JID processing was somewhat loosely defined by the Jabber community
(documentation of forbidden characters and case handling is contained
in "JEP-0029: Definition of Jabber Identifiers", published by the
Jabber Software Foundation [JSF]). XMPP specifies the use of
[NAMEPREP] for domain identifiers and supplements Nameprep with two
additional [STRINGPREP] profiles for JID processing: Nodeprep
(Appendix A) for node identifiers and Resourceprep (Appendix B) for
resource identifiers .
D.5 Error Handling
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Stream-related errors are handled in the Jabber community via simple
CDATA text in a <stream:error/> element. In XMPP, stream-related
errors are handled via an extensible mechanism defined under Stream
Errors (Section 4.6) herein.
Stanza-related errors are handled in the Jabber community via
HTTP-style error codes. In XMPP, stanza-related errors are handled
via an extensible mechanism defined under Stanza Errors (Section 9.3)
herein. (Documentation of a mapping between Jabber and XMPP error
handling mechanisms is contained in "JEP-0086: Legacy Errors",
published by the Jabber Software Foundation [JSF].)
D.6 Internationalization
Although use of UTF-8 has always been standard practice within the
Jabber community, the community did not define mechanisms for
specifying the language of human-readable text provided in CDATA
sections. XMPP specifies the use of the 'xml:lang' attribute in such
contexts, as defined under Stream Attributes (Section 4.2) and
xml:lang (Section 9.1.5) herein.
D.7 Stream Version Attribute
The Jabber community does not include a 'version' attribute in stream
headers. XMPP specifies inclusion of that attribute, with a value of
'1.0', as a way to signal support for the stream features
(authentication, encryption, etc.) defined under Version Support
(Section 4.2.1) herein.
Appendix E. Revision History
Note to RFC Editor: please remove this entire appendix, and the
corresponding entries in the table of contents, prior to publication.
E.1 Changes from draft-ietf-xmpp-core-20
o Completed changes necessary to address IESG feedback.
E.2 Changes from draft-ietf-xmpp-core-19
o Fixed several typographical errors.
o Restricted values of 'type' attribute for IQ stanzas to those
defined in the schema (i.e., changed SHOULD to MUST) to ensure
consistency with text in XMPP IM.
o Added reference to RFC 3548.
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o Added the <not-authorized/> stanza error.
o Replaced RFC 2222 reference with reference to
draft-ietf-sasl-rfc2222bis.
o Further clarified role and usage of user names in SASL mechanisms.
o Added mention of 'code' attribute on error element.
o Clarified several sentences in the dialback narrative.
o Clarified use of stringprep profiles and added reference to RFC
3490.
o Added security consideration regarding lack of SASL channel
binding to TLS per discussion at IETF 58 meeting.
o Adjusted formatting to conform to RFC Editor requirements.
E.3 Changes from draft-ietf-xmpp-core-18
o Added the 'xml:lang' attribute to the root <stream/> element per
previous consensus and list discussion.
o Changed "jabber-server" and "jabber-client" service names to
"xmpp-server" and "xmpp-client".
o Added the <gone/>, <not-acceptable/>, and <redirect/> stanza
errors.
o Changed dataype of <see-other-host/> stream error and of <gone/>
and <redirect/> stanza errors to xs:string so that these elements
may contain programmatic information.
o Removed <invalid-realm/> and <bad-protocol/> SASL errors.
o Removed references to RFC 952 and RFC 1123 (domain name format is
handled by reference to Nameprep).
o Changed address record resolution text so that it is not specific
to IPv4.
o Clarified text in appendices regarding scope of Nodeprep and
Resourceprep.
o Removed requirement that receiving entity terminate the TCP
connection upon receiving an <abort/> element from or sending a
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<failure/> element to the initiating entity during SASL
negotiation.
o Removed recommendation that TLS and SASL security layer should not
both be used simultaneously.
o Added subsection to Security Considerations regarding use of
base64 in SASL.
o Specified rules regarding inclusion of username in SASL
negotiation.
o Adjusted content related to SASL authorization identities, since
the previous text did not track SASL.
o Added section on resource binding to compensate for changes to
SASL authorization identity text.
o Specified ABNF for JIDs.
o Checked all references.
o Completed a thorough proofreading and consistency check of the
entire text.
E.4 Changes from draft-ietf-xmpp-core-17
o Specified that UTF-8 is the only allowable encoding.
o Added stream errors for <bad-namespace-prefix/>, <invalid-xml/>,
and <restricted-xml/>, as well as a <bad-format/> error for
generic XML error conditions.
o Folded Nodeprep and Resourceprep profiles into this document.
o Moved most delivery handling rules from XMPP IM to XMPP Core.
o Moved detailed stanza syntax descriptions from XMPP Core to XMPP
IM.
o Moved stanza schemas from XMPP Core to XMPP IM.
E.5 Changes from draft-ietf-xmpp-core-16
o Added <conflict/> and <unsupported-encoding/> stream errors.
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o Changed the datatype for the <see-other-host/> and
<unsupported-version/> stream errors from 'xs:string' to 'empty'.
o Further clarified server handling of the basic stanza kinds.
o Further clarified character encoding rules per list discussion.
o Specified meaning of version='1.0' flag in stream headers.
o Added stream closure to SASL failure cases in order to mirror
handling of TLS failures.
o Added section on compliance requirements for server and client
implementations.
o Added non-normative section on differences between Jabber usage
and XMPP specifications.
E.6 Changes from draft-ietf-xmpp-core-15
o Added <connection-timeout/> and <policy-violation/> stream errors.
o Added <aborted/> SASL error and clarified <bad-protocol/> error.
o Made 'id' required for IQ stanzas.
E.7 Changes from draft-ietf-xmpp-core-14
o Added SRV lookup for client-to-server communications.
o Changed server SRV record to conform to RFC 2782; specifically,
the service identifier was changed from 'jabber' to
'jabber-server'.
E.8 Changes from draft-ietf-xmpp-core-13
o Clarified stream restart after successful TLS and SASL
negotiation.
o Clarified requirement for resolution of DNS hostnames.
o Clarified text regarding namespaces.
o Clarified examples regarding empty <stream:features/> element.
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o Added several more SASL error conditions.
o Changed <invalid-xml/> stream error to <improper-addressing/> and
added to schema.
o Made small editorial changes and fixed several schema errors.
E.9 Changes from draft-ietf-xmpp-core-12
o Moved server dialback to a separate section; clarified its
security characteristics and its role in the protocol.
o Adjusted error handling syntax and semantics per list discussion.
o Further clarified length of node identifiers and total length of
JIDs.
o Documented message type='normal'.
o Corrected several small errors in the TLS and SASL sections.
o Corrected several errors in the schemas.
E.10 Changes from draft-ietf-xmpp-core-11
o Corrected several small errors in the TLS and SASL sections.
o Made small editorial changes and fixed several schema errors.
E.11 Changes from draft-ietf-xmpp-core-10
o Adjusted TLS content regarding certificate validation process.
o Specified that stanza error extensions for specific applications
are to be properly namespaced children of the relevant descriptive
element.
o Clarified rules for inclusion of the 'id' attribute.
o Specified that the 'xml:lang' attribute SHOULD be included (per
list discussion).
o Made small editorial changes and fixed several schema errors.
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E.12 Changes from draft-ietf-xmpp-core-09
o Fixed several dialback error conditions.
o Cleaned up rules regarding TLS and certificate processing based on
off-list feedback.
o Changed <stream-condition/> and <stanza-condition/> elements to
<condition/>.
o Added or modified several stream and stanza error conditions.
o Specified only one child allowed for IQ, or two if type="error".
o Fixed several errors in the schemas.
E.13 Changes from draft-ietf-xmpp-core-08
o Incorporated list discussion regarding addressing, SASL, TLS, TCP,
dialback, namespaces, extensibility, and the meaning of 'ignore'
for routers and recipients.
o Specified dialback error conditions.
o Made small editorial changes to address RFC Editor requirements.
E.14 Changes from draft-ietf-xmpp-core-07
o Made several small editorial changes.
E.15 Changes from draft-ietf-xmpp-core-06
o Added text regarding certificate validation in TLS negotiation per
list discussion.
o Clarified nature of XML restrictions per discussion with W3C, and
moved XML Restrictions subsection under "XML Usage within XMPP".
o Further clarified that XML streams are unidirectional.
o Changed stream error and stanza error namespace names to conform
to the format defined in The IETF XML Registry.
o Removed note to RFC Editor regarding provisional namespace names.
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E.16 Changes from draft-ietf-xmpp-core-05
o Added <invalid-namespace/> as a stream error condition.
o Adjusted security considerations per discussion at IETF 56 and on
list.
E.17 Changes from draft-ietf-xmpp-core-04
o Added server-to-server examples for TLS and SASL.
o Changed error syntax, rules, and examples based on list
discussion.
o Added schemas for the TLS, stream error, and stanza error
namespaces.
o Added note to RFC Editor regarding provisional namespace names.
o Made numerous small editorial changes and clarified text
throughout.
E.18 Changes from draft-ietf-xmpp-core-03
o Clarified rules and procedures for TLS and SASL.
o Amplified stream error code syntax per list discussion.
o Made numerous small editorial changes.
E.19 Changes from draft-ietf-xmpp-core-02
o Added dialback schema.
o Removed all DTDs since schemas provide more complete definitions.
o Added stream error codes.
o Clarified error code "philosophy".
E.20 Changes from draft-ietf-xmpp-core-01
o Updated the addressing restrictions per list discussion and added
references to the new Nodeprep and Resourceprep profiles.
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o Corrected error in Use of SASL regarding 'version' attribute.
o Made numerous small editorial changes.
E.21 Changes from draft-ietf-xmpp-core-00
o Added information about TLS from list discussion.
o Clarified meaning of "ignore" based on list discussion.
o Clarified information about Universal Character Set data and
character encodings.
o Provided base64-decoded information for examples.
o Fixed several errors in the schemas.
o Made numerous small editorial fixes.
E.22 Changes from draft-miller-xmpp-core-02
o Brought Use of SASL section into line with discussion on list and
at IETF 55 meeting.
o Added information about the optional 'xml:lang' attribute per
discussion on list and at IETF 55 meeting.
o Specified that validation is neither required nor recommended, and
that the formal definitions (DTDs and schemas) are included for
descriptive purposes only.
o Specified that the response to an IQ stanza of type "get" or "set"
must be an IQ stanza of type "result" or "error".
o Specified that compliant server implementations must process
stanzas in order.
o Specified that for historical reasons some server implementations
may accept 'stream:' as the only valid namespace prefix on the
root stream element.
o Clarified the difference between 'jabber:client' and
'jabber:server' namespaces, namely, that 'to' and 'from'
attributes are required on all stanzas in the latter but not the
former.
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o Fixed typo in Step 9 of the dialback protocol (changed db:result
to db:verify).
o Removed references to TLS pending list discussion.
o Removed the non-normative appendix on OpenPGP usage pending its
inclusion in a separate I-D.
o Simplified the architecture diagram, removed most references to
services, and removed references to the 'jabber:component:*'
namespaces.
o Noted that XMPP activity respects firewall administration
policies.
o Further specified the scope and uniqueness of the 'id' attribute
in all stanza kinds and the <thread/> element in message stanzas.
o Nomenclature changes: (1) from "chunks" to "stanzas"; (2) from
"host" to "server" and from "node" to "client" (except with regard
to definition of the addressing scheme).
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgment
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Saint-Andre (ed.) Expires July 6, 2004 [Page 95]
XMPP Working Group P. Saint-Andre (ed.)
Internet-Draft Jabber Software Foundation
Expires: July 6, 2004 January 6, 2004
Extensible Messaging and Presence Protocol (XMPP): Instant Messaging
and Presence
draft-ietf-xmpp-im-20
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at http://
www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on July 6, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This memo describes extensions to and applications of the core
features of the Extensible Messaging and Presence Protocol (XMPP)
that provide the basic instant messaging (IM) and presence
functionality defined in RFC 2779.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Syntax of XML Stanzas . . . . . . . . . . . . . . . . . . . 4
3. Session Establishment . . . . . . . . . . . . . . . . . . . 11
4. Exchanging Messages . . . . . . . . . . . . . . . . . . . . 14
5. Exchanging Presence Information . . . . . . . . . . . . . . 16
6. Managing Subscriptions . . . . . . . . . . . . . . . . . . . 25
7. Roster Management . . . . . . . . . . . . . . . . . . . . . 26
8. Integration of Roster Items and Presence Subscriptions . . . 31
9. Subscription States . . . . . . . . . . . . . . . . . . . . 54
10. Blocking Communication . . . . . . . . . . . . . . . . . . . 59
11. Server Rules for Handling XML Stanzas . . . . . . . . . . . 79
12. IM and Presence Compliance Requirements . . . . . . . . . . 81
13. Internationalization Considerations . . . . . . . . . . . . 82
14. Security Considerations . . . . . . . . . . . . . . . . . . 82
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . 83
Normative References . . . . . . . . . . . . . . . . . . . . 84
Informative References . . . . . . . . . . . . . . . . . . . 85
Author's Address . . . . . . . . . . . . . . . . . . . . . . 85
A. vCards . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
B. XML Schemas . . . . . . . . . . . . . . . . . . . . . . . . 86
C. Differences Between Jabber IM/Presence and XMPP . . . . . . 98
D. Revision History . . . . . . . . . . . . . . . . . . . . . . 99
Intellectual Property and Copyright Statements . . . . . . . 106
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1. Introduction
1.1 Overview
The Extensible Messaging and Presence Protocol (XMPP) is a protocol
for streaming XML [XML] elements in order to exchange messages and
presence information in close to real time. The core features of
XMPP are defined in Extensible Messaging and Presence Protocol
(XMPP): Core [XMPP-CORE]. These features -- mainly XML streams, use
of TLS and SASL, and the <message/>, <presence/>, and <iq/> children
of the stream root -- provide the building blocks for many types of
near-real-time applications, which may be layered on top of the core
by sending application-specific data qualified by particular XML
namespaces [XML-NAMES]. This memo describes extensions to and
applications of the core features of XMPP that provide the basic
functionality expected of an instant messaging (IM) and presence
application as defined in RFC 2779 [IMP-REQS].
1.2 Requirements
For the purposes of this memo, the requirements of a basic instant
messaging and presence application are defined by [IMP-REQS], which
at a high level stipulates that a user must be able to complete the
following use cases:
o Exchange messages with other users
o Exchange presence information with other users
o Manage subscriptions to and from other users
o Manage items in a contact list (in XMPP this is called a "roster")
o Block communications to or from specific other users
Detailed definitions of these functionality areas are contained in
[IMP-REQS], and the interested reader is directed to that document
regarding the requirements addressed herein.
[IMP-REQS] also stipulates that presence services must be separable
from instant messaging services; i.e., it must be possible to use the
protocol to provide a presence service, an instant messaging service,
or both. Although the text of this memo assumes that implementations
and deployments will want to offer a unified instant messaging and
presence service, there is no requirement that a service must offer
both a presence service and an instant messaging service, and the
protocol makes it possible to offer separate and distinct services
for presence and for instant messaging.
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Note: While XMPP-based instant messaging and presence meets the
requirements of [IMP-REQS], it was not designed explicitly with that
specification in mind, since the base protocol evolved through an
open development process within the Jabber open-source community
before RFC 2779 was written. Note also that although protocols
addressing many other functionality areas have been defined in the
Jabber community, such protocols are not included in this memo
because they are not required by [IMP-REQS].
1.3 Terminology
This memo inherits the terminology defined in [XMPP-CORE].
The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [TERMS].
1.4 Contributors
Most of the core aspects of the Extensible Messaging and Presence
Protocol were developed originally within the Jabber open-source
community in 1999. This community was founded by Jeremie Miller, who
released source code for the initial version of the jabberd server in
January 1999. Major early contributors to the base protocol also
included Ryan Eatmon, Peter Millard, Thomas Muldowney, and Dave
Smith. Work specific to instant messaging and presence by the XMPP
Working Group has concentrated especially on IM session establishment
and communication blocking (privacy rules); the session establishment
protocol was mainly developed by Rob Norris and Joe Hildebrand, and
the privacy rules protocol was originally contributed by Peter
Millard.
1.5 Acknowledgements
Thanks are due to a number of individuals in addition to the
contributors listed. Although it is difficult to provide a complete
list, the following individuals were particularly helpful in defining
the protocols or in commenting on the specifications in this memo:
Thomas Charron, Richard Dobson, Schuyler Heath, Jonathan Hogg, Craig
Kaes, Jacek Konieczny, Alexey Melnikov, Keith Minkler, Julian Missig,
Pete Resnick, Marshall Rose, Alexey Shchepin, Jean-Louis Seguineau,
Iain Shigeoka, and David Waite. Thanks also to members of the XMPP
Working Group and the IETF community for comments and feedback
provided throughout the life of this memo.
2. Syntax of XML Stanzas
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The basic semantics and common attributes of XML stanzas qualified by
the 'jabber:client' and 'jabber:server' namespaces are defined in
[XMPP-CORE]. However, these namespaces also define various child
elements, as well as values for the common 'type' attribute, that are
specific to instant messaging and presence applications. Thus,
before addressing particular "use cases" for such applications, we
here further describe the syntax of XML stanzas, thereby
supplementing the discussion in [XMPP-CORE].
2.1 Message Syntax
Message stanzas in the 'jabber:client' or 'jabber:server' namespace
are used to "push" information to another entity. Common uses in
instant messaging applications include single messages, messages sent
in the context of a chat conversation, messages sent in the context
of a multi-user chat room, headlines, and errors.
2.1.1 Types of Message
The 'type' attribute of a message stanza is RECOMMENDED; if included,
it specifies the conversational context of the message, thus
providing a hint regarding presentation (e.g., in a GUI). If
included, the 'type' attribute MUST have one of the following values:
o chat -- The message is sent in the context of a one-to-one chat
conversation. A compliant client SHOULD present the message an
interface enabling one-to-one chat between the two parties,
including an appropriate conversation history.
o error -- An error has occurred related to a previous message sent
by the sender (for details regarding stanza error syntax, refer to
[XMPP-CORE]). A compliant client SHOULD present an appropriate
interface informing the sender of the nature of the error.
o groupchat -- The message is sent in the context of a multi-user
chat environment. A compliant client SHOULD present the message
an interface enabling many-to-many chat between the parties,
including a roster of parties in the chatroom and an appropriate
conversation history. Full definition of XMPP-based groupchat
protocols is out of scope for this memo.
o headline -- The message is probably generated by an automated
service that delivers or broadcasts content (news, sports, market
information, RSS feeds, etc.). No reply to the message is
expected, and a compliant client SHOULD present the message 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).
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o normal -- The message is a single message that is sent outside the
context of a one-to-one conversation or groupchat, and to which it
is expected that the recipient will reply. A compliant client
SHOULD present the message in an interface enabling the recipient
to reply.
An IM application SHOULD support all of the foregoing message types;
if an application receives a message with no 'type' attribute or the
application does not understand the value of the 'type' attribute
provided, it MUST consider the message to be of type "normal" (i.e.,
"normal" is the default). The "error" type MUST be generated only in
response to an error related to a message received from another
entity.
Although the 'type' attribute is NOT REQUIRED, it is considered
polite to mirror the type in any replies to a message; furthermore,
some specialized applications (e.g., a multi-user chat service) MAY
at their discretion enforce the use of a particular message type
(e.g., type='groupchat').
2.1.2 Child Elements
As described under extended namespaces (Section 2.4), a message
stanza MAY contain any properly-namespaced child element.
In accordance with the default namespace declaration, by default a
message stanza is in the 'jabber:client' or 'jabber:server'
namespace, which defines certain allowable children of message
stanzas. If the message stanza is of type "error", it MUST include
an <error/> child; for details, see [XMPP-CORE]. Otherwise, the
message stanza MAY contain any of the following child elements
without an explicit namespace declaration:
1. <subject/>
2. <body/>
3. <thread/>
2.1.2.1 Subject
The <subject/> element contains XML character data that specifies the
topic of the message. The <subject/> element MUST NOT possess any
attributes, with the exception of the 'xml:lang' attribute. Multiple
instances of the <subject/> element MAY be included for the purpose
of providing alternate versions of the same subject, but only if each
instance possesses an 'xml:lang' attribute with a distinct language
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value. The <subject/> element MUST NOT contain mixed content (as
defined in Section 3.2.2 of [XML]).
2.1.2.2 Body
The <body/> element contains XML character data that specifies the
textual contents of the message; this child element is normally
included but NOT REQUIRED. The <body/> element MUST NOT possess any
attributes, with the exception of the 'xml:lang' attribute. Multiple
instances of the <body/> element MAY be included but only if each
instance possesses an 'xml:lang' attribute with a distinct language
value. The <body/> element MUST NOT contain mixed content (as
defined in Section 3.2.2 of [XML]).
2.1.2.3 Thread
The <thread/> element contains XML character data that specifies an
identifier that is used for tracking a conversation thread (sometimes
referred to as an "instant messaging session") between two entities.
The value of the <thread/> element is generated by the sender and
that SHOULD be copied back in any replies. If used, it MUST be
unique to that conversation thread within the stream and MUST be
consistent throughout that conversation (a client that receives a
message from the same full JID but with a different thread ID MUST
assume that the message in question exists outside the context of the
existing conversation thread). The use of the <thread/> element is
OPTIONAL and is not used to identify individual messages, only
conversations. A message stanza MUST NOT contain more than one
<thread/> element. The <thread/> element MUST NOT possess any
attributes. The value of the <thread/> element MUST be treated as
opaque by entities; no semantic meaning may be derived from it, and
only exact comparisons may be made against it. The <thread/> element
MUST NOT contain mixed content (as defined in Section 3.2.2 of
[XML]).
2.2 Presence Syntax
Presence stanzas are used in the 'jabber:client' or 'jabber:server'
namespace to express an entity's current availability status (offline
or online, along with various sub-states of the latter and optional
user-defined descriptive text), and to communicate that status to
other entities. Presence stanzas are also used to negotiate and
manage subscriptions to the presence of other entities.
2.2.1 Types of Presence
The 'type' attribute of a presence stanza is OPTIONAL. A presence
stanza that does not possess a 'type' attribute is used to signal to
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the server that the sender is online and available for communication.
If included, the 'type' attribute specifies a lack of availability, a
request to manage a subscription to another entity's presence, a
request for another entity's current presence, or an error related to
a previously-sent presence stanza. If included, the 'type' attribute
MUST have one of the following values:
o unavailable -- Signals that the entity is no longer available for
communication.
o subscribe -- The sender wishes to subscribe to the recipient's
presence.
o subscribed -- The sender has allowed the recipient to receive
their presence.
o unsubscribe -- A notification that an entity is unsubscribing from
another entity's presence.
o unsubscribed -- The subscription request has been denied or a
previously-granted subscription has been cancelled.
o probe -- A request for an entity's current presence; SHOULD be
generated only by a server and SHOULD NOT be generated by a
client.
o error -- An error has occurred regarding processing or delivery of
a previously-sent presence stanza.
For detailed information regarding presence semantics and the
subscription model used in the context of XMPP-based instant
messaging and presence applications, refer to Exchanging Presence
Information (Section 5) and Managing Subscriptions (Section 6).
2.2.2 Child Elements
As described under extended namespaces (Section 2.4), a presence
stanza MAY contain any properly-namespaced child element.
In accordance with the default namespace declaration, by default a
presence stanza is in the 'jabber:client' or 'jabber:server'
namespace, which defines certain allowable children of presence
stanzas. If the presence stanza is of type "error", it MUST include
an <error/> child; for details, see [XMPP-CORE]. If the presence
stanza possesses no 'type' attribute, it MAY contain any of the
following child elements (note that the <status/> child MAY be sent
in a presence stanza of type "unavailable" or, for historical
reasons, "subscribe"):
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1. <show/>
2. <status/>
3. <priority/>
2.2.2.1 Show
The OPTIONAL <show/> element contains XML character data that
specifies the particular availability status of an entity or specific
resource. A presence stanza MUST NOT contain more than one <show/>
element. The <show/> element MUST NOT possess any attributes. The
XML character data contained in the <show/> element is not intended
to be human-readable. If provided, the CDATA value MUST be one of
the following (additional availability types could be defined through
a properly-namespaced child element of the presence stanza):
o away -- The entity or resource is temporarily away.
o chat -- The entity or resource is actively interested in chatting.
o xa -- The entity or resource is away for an extended period (xa =
"eXtended Away").
o dnd -- The entity or resource is busy (dnd = "Do Not Disturb").
If no <show/> element is provided, the entity is assumed to be online
and available.
2.2.2.2 Status
The OPTIONAL <status/> element contains a natural-language
description of availability status. It is normally used in
conjunction with the show element to provide a detailed description
of an availability state (e.g., "In a meeting"). The <status/>
element MUST NOT possess any attributes, with the exception of the
'xml:lang' attribute. Multiple instances of the <status/> element
MAY be included but only if each instance possesses an 'xml:lang'
attribute with a distinct language value.
2.2.2.3 Priority
The OPTIONAL <priority/> element contains XML character data that
specifies the priority level of the resource. The value may be any
integer between -128 and +127. A presence stanza MUST NOT contain
more than one <priority/> element. The <priority/> element MUST NOT
possess any attributes. If no priority is provided, a server SHOULD
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consider the priority to be zero. For information regarding the
semantics of priority values in stanza routing within instant
messaging and presence applications, refer to Server Rules for
Handling XML Stanzas (Section 11).
2.3 IQ Syntax
IQ stanzas provide a structured request-response mechanism. The
basic semantics of that mechanism 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). This memo defines two such extended
namespaces, one for Roster Management (Section 7) and the other for
Blocking Communication (Section 10); however, an IQ stanza MAY
contain structured information qualified by any extended namespace.
2.4 Extended Namespaces
While the three XML stanza kinds defined in the "jabber:client" or
"jabber:server" namespace (along with their attributes and child
elements) provide a basic level of functionality for messaging and
presence, XMPP uses XML namespaces to extend the stanzas for the
purpose of providing additional functionality. Thus a message or
presence MAY contain one or more optional child elements containing
content that extends the meaning of the message (e.g., an
XHTML-formatted version of the message body), and an IQ stanza MAY
contain one such child element. This child element MAY have any name
and MUST possess an 'xmlns' namespace declaration (other than
"jabber:client", "jabber:server", or "http://etherx.jabber.org/
streams") that defines all data contained within the child element.
Support for any given extended namespace is OPTIONAL on the part of
any implementation (aside from the extended namespaces defined
herein). If an entity does not understand such a namespace, the
entity's expected behavior depends on whether the entity is (1) the
recipient or (2) an entity that is routing the stanza to the
recipient:
Recipient: If a recipient receives a stanza that contains a child
element it does not understand, it SHOULD ignore that specific XML
data, i.e., it SHOULD not process it or present it to a user or
associated application (if any). In particular:
* 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.
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* 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 <feature-not-implemented/>.
Router: If a routing entity (usually a server) handles a stanza that
contains a child element it does not understand, it SHOULD ignore
the associated XML data by passing it on untouched to the
recipient.
3. Session Establishment
Most instant messaging and presence applications based on XMPP are
implemented via a client-server architecture that requires a client
to establish a session on a server in order to engage in the expected
instant messaging and presence activities. However, there are
several pre-conditions that MUST be met before a client can establish
an instant messaging and presence session. These are:
1. Stream Authentication -- a client MUST complete stream
authentication as documented in [XMPP-CORE] before attempting to
establish a session or send any XML stanzas.
2. Resource Binding -- after completing stream authentication, a
client MUST bind a resource to the stream so that the client's
address is of the form <user@domain/resource>, after which the
entity is said to be a "connected resource" in the terminology of
[XMPP-CORE].
If a server supports sessions, it MUST include a <session/> element
qualified by the 'urn:ietf:params:xml:ns:xmpp-session' namespace in
the stream features it advertises to a client after the completion of
stream authentication as defined in [XMPP-CORE]:
Server advertises session establishment feature to client:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='c2s_345'
from='example.com'
version='1.0'>
<stream:features>
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<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<session xmlns='urn:ietf:params:xml:ns:xmpp-session'>
</stream:features>
Upon being so informed that session establishment is required (and
after completing resource binding), the client MUST establish a
session if it desires to engage in instant messaging and presence
functionality; it completes this step by sending to the server an IQ
stanza of type "set" containing an empty <session/> child element
qualified by the 'urn:ietf:params:xml:ns:xmpp-session' namespace:
Step 1: Client requests session with server:
<iq from='someuser@example.com'
to='example.com'
type='set'
id='sess_1'>
<session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
</iq>
Step 2: Server informs client that session has been created:
<iq from='example.com'
to='someuser@example.com'
type='result'
id='sess_1'/>
Upon establishing a session, a connected resource (in the terminology
of [XMPP-CORE]) is said to be an "active resource".
Several error conditions are possible. For example, the server may
encounter an internal condition that prevents it from creating the
session, the username or authorization identity may lack permissions
to create a session, or there may already be an active resource
associated with a resource identifier of the same name.
If the server encounters an internal condition that prevents it from
creating the session, it MUST return an error.
Step 2 (alt): Server responds with error (internal server error):
<iq type='error' id='sess_1'>
<session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
<error type='wait'>
<internal-server-error
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
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If the username or resource is not allowed to create a session, the
server MUST return an error (e.g., forbidden).
Step 2 (alt): Server responds with error (username or resource not
allowed to create session):
<iq type='error' id='sess_1'>
<session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
<error type='auth'>
<forbidden
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
If there is already an active resource of the same name, the server
MUST either (1) terminate the active resource and allow the
newly-requested session, or (2) disallow the newly-requested session
and maintain the active resource. Which of these the server does is
up to the implementation, although it is RECOMMENDED to implement
case #1. In case #1, the server SHOULD send a <conflict/> stream
error to the active resource, terminate the XML stream and underlying
TCP connection for the active resource, and return a IQ stanza of
type "result" (indicating success) to the newly-requested session. In
case #2, the server SHOULD send a <conflict/> stanza error to the
newly-requested session but maintain the XML stream for that
connection so that the newly-requested session has an opportunity to
negotiate a non-conflicting resource identifier before sending
another request for session establishment.
Step 2 (alt): Server informs active resource of resource conflict
(case #1):
<stream:error>
<conflict xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
Step 2 (alt): Server informs newly-requested session of resource
conflict (case #2):
<iq type='error' id='sess_1'>
<session xmlns='urn:ietf:params:xml:ns:xmpp-session'/>
<error type='cancel'>
<conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
After establishing a session, a client SHOULD send initial presence
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and request its roster as described below, although these actions are
NOT REQUIRED.
Note: Before allowing the creation of instant messaging and presence
sessions, a server MAY require prior account provisioning. Possible
methods for account provisioning include account creation by a server
administrator as well as in-band account registration using the
'jabber:iq:register' namespace; the latter method is documented by
the Jabber Software Foundation [JSF] at <http://www.jabber.org/
protocol/> but is out of scope for this memo.
4. Exchanging Messages
Exchanging messages is a basic use of XMPP and is brought about when
a user generates a message stanza that is addressed to another
entity. As defined under Server Rules for Handling XML Stanzas
(Section 11), the sender's server is responsible for delivering the
message to the intended recipient (if the recipient is on the same
server) or for routing the message to the recipient's server (if the
recipient is on a different server).
For information regarding the syntax of message stanzas as well as
their defined attributes and child elements, refer to Message Syntax
(Section 2.1).
4.1 Specifying an Intended Recipient
An instant messaging client SHOULD specify an intended recipient for
a message by providing the JID of an entity other than the sender in
the 'to' attribute of the <message/> stanza. If the message is being
sent in reply to a message previously received from an address of the
form <user@domain/resource> (e.g., within the context of a chat
session), the value of the 'to' address SHOULD be the full JID (of
the form <user@domain/resource>) rather than merely of the form
<user@domain> unless the sender has knowledge (via presence) that the
intended recipient's resource is no longer available. If the message
is being sent outside the context of any existing chat session or
received message, the value of the 'to' address SHOULD be of the form
<user@domain> rather than of the form <user@domain/resource>.
4.2 Specifying a Message Type
As noted, it is RECOMMENDED for a message stanza to possess a 'type'
attribute whose value captures the conversational context (if any) of
the message (see Type (Section 2.1.1)).
The following example shows a valid value of the 'type' attribute:
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Example: A message of a defined type:
<message
to='romeo@example.net'
from='juliet@example.com/balcony'
type='chat'
xml:lang='en'>
<body>Wherefore art thou, Romeo?</body>
</message>
4.3 Specifying a Message Body
A message stanza MAY (and often will) contain a child <body/> element
whose XML character data specifies the primary meaning of the message
(see Body (Section 2.1.2.2)).
Example: A message with a body:
<message
to='romeo@example.net'
from='juliet@example.com/balcony'
type='chat'
xml:lang='en'>
<body>Wherefore art thou, Romeo?</body>
<body xml:lang='cz'>PročeŽ jsi ty, Romeo?</body>
</message>
4.4 Specifying a Message Subject
A message stanza MAY contain one or more child <subject/> elements
specifying the topic of the message (see Subject (Section 2.1.2.1)).
Example: A message with a subject:
<message
to='romeo@example.net'
from='juliet@example.com/balcony'
type='chat'
xml:lang='en'>
<subject>I implore you!</subject>
<subject
xml:lang='cz'>Úpěnlivě prosim!</subject>
<body>Wherefore art thou, Romeo?</body>
<body xml:lang='cz'>PročeŽ jsi ty, Romeo?</body>
</message>
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4.5 Specifying a Conversation Thread
A message stanza MAY contain a child <thread/> element specifying the
conversation thread in which the message is situated, for the purpose
of tracking the conversation (see Thread (Section 2.1.2.3)).
Example: A threaded conversation:
<message
to='romeo@example.net/orchard'
from='juliet@example.com/balcony'
type='chat'>
<body>Art thou not Romeo, and a Montague?</body>
<thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
</message>
<message
to='juliet@example.com/balcony'
from='romeo@example.net/orchard'
type='chat'>
<body>Neither, fair saint, if either thee dislike.</body>
<thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
</message>
<message
to='romeo@example.net/orchard'
from='juliet@example.com/balcony'
type='chat'>
<body>How cam'st thou hither, tell me, and wherefore?</body>
<thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
</message>
5. Exchanging Presence Information
Exchanging presence information is made relatively straightforward
within XMPP by using presence stanzas. However, we see here a
contrast to the handling of messages: although a client MAY send
directed presence information to another entity, normally presence
information is sent from a client to its server (with no 'to'
address) 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], we can say that the only watchers in XMPP
are subscribers). (Note: While presence information MAY be provided
on a user's behalf by an automated service, normally it is provided
by the user's client.)
For information regarding the syntax of presence stanzas as well as
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their defined attributes and child elements, refer to [XMPP-CORE].
5.1 Client and Server Presence Responsibilities
After establishing a session, a client SHOULD (but is NOT REQUIRED
to) 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 handled by the server on behalf of the client) and (2)
MUST possess no 'type' attribute (signalling the user's
availability). After sending initial presence, an active resource is
said to be an "available resource".
Upon receiving initial presence from a client, the user's server MUST
do the following if there is not already one or more available
resources for the user (if there is already one or more available
resources for the user, the server obviously does not need to send
the presence probes, since it already possesses the requisite
information):
1. Send presence probes (i.e., presence stanzas whose 'type'
attribute is set to a value of "probe") from the full JID (e.g.,
<user@example.com/resource>) of the user to the bare JID (e.g.,
<contact@example.org>) of any contacts to which the user is
subscribed in order to determine if they are available; such
contacts are those which are present in the user's roster with
the 'subscription' attribute set to a value of "to" or "both".
2. Broadcast initial presence from the full JID (e.g.,
<user@example.com/resource>) of the user to the bare JID (e.g.,
<contact@example.org>) of any contacts that are subscribed to the
user's presence; such contacts are those which are present in the
user's roster with the 'subscription' attribute set to a value of
"from" or "both".
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 a presence probe from the user, the contact's server
SHOULD reply as follows:
1. If the user is not in the contact's roster with a subscription
state of "From", "From + Pending Out", or "Both" (as defined
under Subscription States (Section 9)), the contact's server MUST
return a presence stanza of type "error" in response to the
presence probe (however, if a server receives a presence probe
from a subdomain of the server's hostname or another such trusted
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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", the contact's
server MUST return a <forbidden/> stanza error in response to
the presence probe.
* if the user is in the contact's roster with a subscription
state of "None + Pending In", "None + Pending Out/In", or "To
+ Pending In", the contact's server MUST return a
<not-authorized/> stanza error in response to the presence
probe.
2. Else, if the contact is blocking presence notifications to the
user's bare JID or full JID (using either a default list or
active list as defined under Blocking Outbound Presence
Notifications (Section 10.11)), the server MUST NOT reply to the
presence probe.
3. Else, if the contact has no available resources, the server MUST
either (1) reply to the presence probe by sending to the user the
full XML of the last presence stanza of type "unavailable"
received by the server from the contact, or (2) not reply at all.
4. Else, if the contact has at least one available resource, the
server MUST reply to the presence probe by sending to the user
the full XML of the last presence stanza received by the server
from each of the contact's available resources (again, subject to
privacy rules for each session).
Upon receiving initial presence from the user, the contact's server
MUST deliver the user's presence stanza to the full JIDs
(<contact@example.org/resource>) associated with all of the contact's
available resources, but only if the user is in the contact's roster
with a subscription state of "to" or "both" and the contact has not
blocked inbound presence notifications from the user's bare or full
JID (as defined under Blocking Inbound Presence Notifications
(Section 10.10)).
If the user's server receives a presence stanza of type "error" in
response to the initial presence that it sent to a contact on behalf
of the user, it SHOULD NOT send further presence updates to that
contact (until and unless it receives a presence stanza from the
contact).
After sending initial presence, the user MAY update its presence
information for broadcasting at any time during its session by
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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 has not blocked outbound presence, 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).
A user MAY send directed presence to another entity (i.e., a presence
stanza with a 'to' attribute whose value is the JID of the other
entity and with either no 'type' attribute or a 'type' attribute
whose value is "unavailable"). There are three possible cases:
1. If the user sends directed presence to a contact that is in the
user's roster with a subscription type of "from" or "both" after
having sent initial presence and before sending unavailable
presence broadcast, the user's server MUST route or deliver the
full XML of that presence stanza (subject to privacy rules) but
SHOULD NOT otherwise modify the contact's status regarding
presence broadcast (i.e., it SHOULD include the contact's JID in
any subsequent presence broadcasts initiated by the user).
2. If the user sends directed presence to an entity that is not in
the user's roster with a subscription type of "from" or "both"
after having sent initial presence and before sending unavailable
presence broadcast, the user's server MUST route or deliver the
full XML of that presence stanza to the entity but MUST NOT
modify the contact's status regarding available presence
broadcast (i.e., it MUST NOT include the entity's JID in any
subsequent broadcasts of available presence initiated by the
user); however, if the available resource from which the user
sent the directed presence become unavailable, the user's server
MUST broadcast that unavailable presence to the entity (if the
user has not yet sent directed unavailable presence to that
entity).
3. If the user sends directed presence without first sending initial
presence or after having sent unavailable presence broadcast
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(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.
Before ending its session with a server, a client SHOULD gracefully
become unavailable by sending a final presence stanza that possesses
no 'to' attribute and that possesses a 'type' attribute whose value
is "unavailable" (optionally, the final presence stanza MAY contain
one or more <status/> elements specifying the reason why the user is
no longer available). However, the user's server MUST NOT depend on
receiving final presence from an available resource, since the
resource may become unavailable unexpectedly. If the user's server
detects that one of the user's resources has become unavailable for
any reason (either gracefully or ungracefully), it MUST broadcast
unavailable presence to all contacts (1) that are in the user's
roster with a subscription type of "from" or "both", (2) to whom the
user has not blocked outbound presence, and (3) from whom the server
has not received a presence error during the user's session; the
user's server MUST also send that unavailable presence stanza to any
of the user's other available resources, as well as to any entities
to which the user has sent directed presence during the user's
session for that resource (if the user has not yet sent directed
unavailable presence to that entity). Any presence stanza with no
'type' attribute and no 'to' attribute that is sent after sending
directed unavailable presence or broadcasted unavailable presence
MUST be broadcasted by the server to all subscribers.
5.2 Specifying Availability Status
A client MAY provide further information about its availability
status by using the <show/> element (see Show (Section 2.2.2.1)).
Example: Availability status:
<presence>
<show>dnd</show>
</presence>
5.3 Specifying Detailed Status Information
In conjunction with the <show/> element, a client MAY provide
detailed status information by using the <status/> element (see
Status (Section 2.2.2.2)).
Example: Detailed status information:
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<presence xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
<status xml:lang='cz'>Ja dvořím Juliet</status>
</presence>
5.4 Specifying Presence Priority
A client MAY provide a priority for its resource by using the
<priority/> element (see Priority (Section 2.2.2.3)).
Example: Presence priority:
<presence xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
<status xml:lang='cz'>Ja dvořím Juliet</status>
<priority>1</priority>
</presence>
5.5 Presence Examples
The examples in this section illustrate the presence-related
protocols described above. The user is romeo@example.net, he has an
available resource whose resource identifier is "orchard", and he has
the following individuals in his roster:
o juliet@example.com (subscription="both" and she has two available
resources, one whose resource is "chamber" and another whose
resource is "balcony")
o benvolio@example.org (subscription="to")
o mercutio@example.org (subscription="from")
Example 1: User sends initial presence:
<presence/>
Example 2: User's server sends presence probes to contacts with
subscription="to" and subscription="both" on behalf of the user's
available resource:
<presence
type='probe'
from='romeo@example.net/orchard'
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to='juliet@example.com'/>
<presence
type='probe'
from='romeo@example.net/orchard'
to='benvolio@example.org'/>
Example 3: User's server sends initial presence to contacts with
subscription="from" and subscription="both" on behalf of the user's
available resource:
<presence
from='romeo@example.net/orchard'
to='juliet@example.com'/>
<presence
from='romeo@example.net/orchard'
to='mercutio@example.org'/>
Example 4: Contacts' server replies to presence probe on behalf of
all of the contact's available resources:
<presence
from='juliet@example.com/balcony'
to='romeo@example.net/orchard'
xml:lang='en'>
<show>away</show>
<status>be right back</status>
<priority>0</priority>
</presence>
<presence
from='juliet@example.com/chamber'
to='romeo@example.net/orchard'>
<priority>1</priority>
</presence>
<presence
from='benvolio@example.org/pda'
to='romeo@example.net/orchard'
xml:lang='en'>
<show>dnd</show>
<status>gallivanting</status>
</presence>
Example 5: Contact's server delivers user's initial presence to all
of the contact's available resources or returns error to user:
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<presence
from='romeo@example.net/orchard'
to='juliet@example.com/chamber'/>
<presence
from='romeo@example.net/orchard'
to='juliet@example.com/balcony'/>
<presence
type='error'
from='mercutio@example.org'
to='romeo@example.net/orchard'>
<error type='cancel'>
<gone xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</presence>
Example 6: User sends directed presence to another user not in his
roster:
<presence
from='romeo@example.net/orchard'
to='nurse@example.com'
xml:lang='en'>
<show>dnd</show>
<status>courting Juliet</status>
<priority>0</priority>
</presence>
Example 7: User sends updated available presence information for
broadcasting:
<presence xml:lang='en'>
<show>away</show>
<status>I shall return!</status>
<priority>1</priority>
</presence>
Example 8: Updated presence information is delivered only to one
contact (not those from whom an error was received or to whom the
user sent directed presence):
<presence
from='romeo@example.net/orchard'
to='juliet@example.com/chamber'
xml:lang='en'>
<show>away</show>
<status>I shall return!</status>
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<priority>1</priority>
</presence>
<presence
from='romeo@example.net/orchard'
to='juliet@example.com/balcony'
xml:lang='en'>
<show>away</show>
<status>I shall return!</status>
<priority>1</priority>
</presence>
Example 9: One of the contact's resources sends final presence:
<presence type='unavailable'/>
Example 10: Contact's server sends unavailable presence information
to user:
<presence
type='unavailable'
from='juliet@example.com/balcony'
to='romeo@example.net/orchard'/>
Example 11: User sends final presence:
<presence type='unavailable' xml:lang='en'>
<status>gone home</status>
</presence>
Example 12: Unavailable presence information is delivered to
contact's one remaining resource as well as to the person to whom the
user sent directed presence:
<presence
type='unavailable'
from='romeo@example.net/orchard'
to='juliet@example.com/chamber'
xml:lang='en'>
<status>gone home</status>
</presence>
<presence
from='romeo@example.net/orchard'
to='nurse@example.com'
xml:lang='en'>
<status>gone home</status>
</presence>
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6. Managing Subscriptions
In order to protect the privacy of instant messaging users and any
other entities, presence and availability information is disclosed
only to other entities that the user has approved. When a user has
agreed that another entity may view its presence, the entity is said
to have a subscription to the user's presence information. A
subscription lasts across sessions; indeed, it lasts until the
subscriber unsubscribes or the subscribee cancels the
previously-granted subscription. Subscriptions are managed within
XMPP by sending presence stanzas containing specially-defined
attributes.
Note: There are important interactions between subscriptions and
rosters; these are defined under Integration of Roster Items and
Presence Subscriptions (Section 8), and the reader must refer to that
section for a complete understanding of presence subscriptions.
6.1 Requesting a Subscription
A request to subscribe to another entity's presence is made by
sending a presence stanza of type "subscribe".
Example: Sending a subscription request:
<presence to='juliet@example.com' type='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
<contact@example.org> rather than <contact@example.org/resource>,
since the desired result is normally for the user to receive presence
from all of the contact's resources, not merely the particular
resource specified in the 'to' attribute.
A user's server MUST NOT automatically approve subscription requests
on the user's behalf. All subscription requests MUST be directed to
the user's client, specifically to one or more available resources
associated with the user. If there is no available resource
associated with the user when the subscription request is received by
the user's server, the user's server MUST keep a record of the
subscription request and deliver the request when the user next
creates an available resource, until the user either approves or
denies the request. If there is more than one available resource
associated with the user when the subscription request is received by
the user's server, the user's server MUST broadcast that subscription
request to all available resources in accordance with Server Rules
for Handling XML Stanzas (Section 11). (Note: If an active resource
has not provided initial presence, the server MUST NOT consider it to
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be available and therefore MUST NOT send subscription requests to
it.) However, f 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 (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.
6.2 Handling a Subscription Request
When a client receives a subscription request from another entity, it
MUST either approve the request by sending a presence stanza of type
"subscribed" or refuse the request by sending a presence stanza of
type "unsubscribed".
Example: Approving a subscription request:
<presence to='romeo@example.net' type='subscribed'/>
Example: Refusing a presence subscription request:
<presence to='romeo@example.net' type='unsubscribed'/>
6.3 Cancelling a Subscription from Another Entity
If a user would like to cancel a previously-granted subscription
request, it sends a presence stanza of type "unsubscribed".
Example: Cancelling a previously granted subscription request:
<presence to='romeo@example.net' type='unsubscribed'/>
6.4 Unsubscribing from Another Entity's Presence
If a user would like to unsubscribe from the presence of another
entity, it sends a presence stanza of type "unsubscribe".
Example: Unsubscribing from an entity's presence:
<presence to='juliet@example.com' type='unsubscribe'/>
7. Roster Management
In XMPP, one's contact list is called a roster, which consists of any
number of specific roster items, each roster item being identified by
a unique JID (usually of the form <contact@example.org>). A user's
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roster is stored by the user's server on the user's behalf so that
the user may access roster information from any resource.
Note: There are important interactions between rosters and
subscriptions; these are defined under Integration of Roster Items
and Presence Subscriptions (Section 8), and the reader must refer to
that section for a complete understanding of roster management.
7.1 Syntax and Semantics
Rosters are managed using IQ stanzas, specifically by means of a
<query/> child element qualified by the 'jabber:iq:roster' namespace.
The <query/> element MAY contain one or more <item/> children, each
describing a unique roster item or "contact".
The "key" or unique identifier for each roster item is a JID,
encapsulated in the required 'jid' attribute of the <item/> element.
The value of the 'jid' attribute SHOULD be of the form <user@domain>,
especially if the item is associated with another (human) instant
messaging user.
The state of the presence subscription in relation to a roster item
is captured in the 'subscription' attribute of the <item/> element.
Allowable values for this attribute are:
o "none" -- the user does not have a subscription to the contact,
and the contact does not have a subscription to the user
o "to" -- the user has a subscription to the contact, but the
contact does not have a subscription to the user
o "from" -- the contact has a subscription to the user, but the user
does not have a subscription to the contact
o "both" -- both the user and the contact have subscriptions to each
other
Each <item/> element MAY contain a 'name' attribute, which sets the
"nickname" to be associated with the JID, as determined by the user
(not the contact). The value of the 'name' attribute is opaque.
Each <item/> element MAY contain one or more <group/> child elements,
for use in collecting roster items into various categories. The
CDATA text of the <group/> element is opaque.
7.2 Business Rules
A server MUST ignore any 'to' address on a roster "set", and MUST
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treat any roster "set" as applying to the sender. For added safety,
a client SHOULD check the "from" address of a roster "push" to ensure
that it is from a trusted source; specifically, the stanza MUST
either have no 'from' attribute (i.e., implicitly from the server) or
have a 'from' attribute whose value matches the user's bare JID (of
the form <user@domain>) or full JID (of the form <user@domain/
resource>); otherwise, the client SHOULD ignore the roster "push".
7.3 Retrieving One's Roster on Login
Upon connecting to the server, a client SHOULD request the roster
(however, because receiving the roster may not be desirable for all
resources, e.g., a connection with limited bandwidth, the client's
request for the roster is NOT REQUIRED). If an available resource
does not request the roster during a session, the server MUST NOT
send it presence subscriptions and associated roster updates.
Example: Client requests current roster from server:
<iq from='juliet@example.com/balcony' type='get' id='roster_1'>
<query xmlns='jabber:iq:roster'/>
</iq>
Example: Client receives roster from the server:
<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'>
<group>Friends</group>
</item>
<item jid='benvolio@example.org'
name='Benvolio'
subscription='both'>
<group>Friends</group>
</item>
</query>
</iq>
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7.4 Adding a Roster Item
At any time, a user MAY add an item to his or her roster.
Example: Client adds a new item:
<iq from='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>
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
set from the server to the client and enables all available resources
to remain in sync with the server-based roster information.
Example: Server (1) pushes the updated roster information to all
available resources that have requested the roster and (2) replies
with an IQ result to the sending resource:
<iq to='juliet@example.com/balcony' type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'
subscription='none'>
<group>Servants</group>
</item>
</query>
</iq>
<iq to='juliet@example.com/chamber' type='set'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com'
name='Nurse'
subscription='none'>
<group>Servants</group>
</item>
</query>
</iq>
<iq to='juliet@example.com/balcony' type='result' id='roster_2'/>
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Example: Connected resources reply with an IQ result to the server:
<iq from='juliet@example.com/balcony'
to='example.com'
type='result'/>
<iq from='juliet@example.com/chamber'
to='example.com'
type='result'/>
7.5 Updating a Roster Item
Updating an existing roster item (e.g., changing the group) is done
in the same way as adding a new roster item, i.e., by sending the
roster item in an IQ set to the server.
Example: User updates roster item (added group):
<iq from='juliet@example.com/chamber' type='set' id='roster_3'>
<query xmlns='jabber:iq:roster'>
<item jid='romeo@example.net'
name='Romeo'
subscription='both'>
<group>Friends</group>
<group>Lovers</group>
</item>
</query>
</iq>
As with adding a roster item, when updating a roster item the server
MUST update the roster information in persistent storage, and also
initiate a roster push to all of the user's available resources that
have requested the roster.
7.6 Deleting a Roster Item
At any time, a user MAY delete an item from its roster by doing an IQ
set and making sure that the value of the 'subscription' attribute is
"remove" (a compliant server MUST ignore any other values of the
'subscription' attribute when received from a client).
Example: Client removes an item:
<iq from='juliet@example.com/balcony' type='set' id='roster_4'>
<query xmlns='jabber:iq:roster'>
<item jid='nurse@example.com' subscription='remove'/>
</query>
</iq>
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As with adding a roster item, when deleting a roster item the server
MUST update the roster information in persistent storage, initiate a
roster push to all of the user's available resources that have
requested the roster (with the 'subscription' attribute set to a
value of "remove"), and send an IQ result to the initiating resource.
For further information about the implications of this command, see
Removing a Roster Item and Cancelling All Subscriptions (Section
8.6).
8. Integration of Roster Items and Presence Subscriptions
8.1 Overview
Some level of integration between roster items and presence
subscriptions is normally expected by an instant messaging user
regarding the user's subscriptions to and from other contacts. This
section describes the level of integration that MUST be supported
within XMPP instant messaging applications.
There are four primary subscription states:
o None -- Neither the user nor the contact is subscribed to the
other's presence
o To -- The user is subscribed to the contact's presence but there
is no subscription from the contact to the user
o From -- There is a subscription from the contact to the user, but
the user has not subscribed to the contact's presence
o Both -- Both the user and the contact are subscribed to each
other's presence (i.e., the union of 'from' and 'to')
Each of these states is reflected in the roster of both the user and
the contact, thus resulting in durable subscription states.
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).
If an active resource does not both send initial presence and request
the roster, the server MUST NOT send it presence subscription
requests or roster pushes.
The 'from' and 'to' addresses are OPTIONAL in roster pushes; if
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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 [XMPP-CORE]).
8.2 User Subscribes to Contact
The process by which a user subscribes to a contact, including the
interaction between roster items and subscription states, is defined
below.
1. In preparation for being able to render the contact in the user's
client interface and for the server to keep track of the
subscription, the user's client SHOULD perform a "roster set" for
the new roster item. This request consists of an IQ stanza of
type='set' containing a <query/> element in the
'jabber:iq:roster' namespace, which in turn contains an <item/>
element that defines the new roster item; the <item/> element
MUST possess a 'jid' attribute, MAY possess a 'name' attribute,
MUST NOT possess a 'subscription' attribute, and MAY contain one
or more <group/> child elements:
<iq type='set' id='set1'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@example.org'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
2. As a result, the user's server (1) MUST initiate a roster push
for the new roster item to all available resources associated
with this user that have requested the roster, setting the
'subscription' attribute to a value of "none"; and (2) MUST reply
with an IQ result related to the roster set:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@example.org'
subscription='none'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
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<iq type='result' id='set1'/>
3. If the user wants to request a subscription to the contact's
presence, the user's client MUST send a presence stanza of
type='subscribe' to the contact:
<presence to='contact@example.org' type='subscribe'/>
4. As a result, the user's server MUST initiate a second roster push
to all of the user's available resources that have requested the
roster, setting the contact to the pending sub-state of the
'none' subscription state; this pending sub-state is denoted by
the inclusion of the ask='subscribe' attribute in the roster
item:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@example.org'
subscription='none'
ask='subscribe'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
Note: If the user did not create a roster item before sending the
subscription request, the server MUST now create one on behalf of
the user with the 'subscription' attribute set to a value of
"none", then send a roster push to all of the user's available
resources that have requested the roster, absent the 'name'
attribute and the <group/> child.
5. The user's server MUST also stamp the presence stanza of type
"subscribe" with the user's bare JID (i.e., <user@example.com>)
as the 'from' address. If the contact is served by a different
host than the user, the user's server MUST route the presence
stanza to the contact's server for delivery to the contact (this
case is assumed throughout; however, if the contact is served by
the same host, then the server can simply deliver the presence
stanza directly):
<presence
from='user@example.com'
to='contact@example.org'
type='subscribe'/>
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Note: If the user's server receives a presence stanza of type
"error" from the contact's server in response to the outgoing
presence stanza of type "subscribe", it MUST revert the
subscription state from the new state ("None + Pending Out") to
the previous state ("None"), and MUST deliver the error stanza to
the user.
6. Upon receiving the presence stanza of type "subscribe" addressed
to the contact, the contact's server MUST determine if there is
at least one available resource from which the contact has
requested the roster. If so, it MUST deliver the subscription
request to the contact (if not, the contact's server MUST store
the subscription request offline for delivery when this condition
is next met; normally this is done by adding a roster item for
the contact to the user's roster, with a state of "None + Pending
In" as defined under Subscription States (Section 9), however a
server SHOULD NOT push or deliver roster items in that state to
the user). No matter when the subscription request is delivered,
the contact must decide whether or not to approve it (subject to
configured preferences, the contact's client MAY approve or
refuse the subscription request without presenting it to the
contact). Here we assume the "happy path" that the contact
approves the subscription request (the alternate flow of
declining the subscription request is defined in Section 8.2.1).
In this case, the contact's client (1) SHOULD perform a roster
set specifying the desired nickname and group for the user (if
any); and (2) MUST send a presence stanza of type "subscribed" to
the user in order to approve the subscription request.
<iq type='set' id='set2'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@example.com'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence to='user@example.com' type='subscribed'/>
7. As a result, the contact's server (1) MUST initiate a roster push
to all available resources associated with the contact that have
requested the roster, containing a roster item for the user with
the subscription state set to 'from' (the server MUST send this
even if the contact did not perform a roster set); (2) MUST
return an IQ result related to the roster set; (3) MUST route the
presence stanza of type "subscribed" to the user; and (4) MUST
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send available presence from all of the contact's available
resources to the user:
<iq type='set' to='contact@example.org/resource'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@example.com'
subscription='from'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<iq type='result' to='contact@example.org/resource' id='set2'/>
<presence
from='contact@example.org/resource'
to='user@example.com'
type='subscribed'/>
<presence
from='contact@example.org/resource'
to='user@example.com'/>
Note: If the contact's server receives a presence stanza of type
"error" from the user's server in response to the outgoing
presence stanza of type "subscribed", it MUST revert the
subscription state from the new state ("From") to the previous
state ("None + Pending In"), and MUST deliver the error stanza to
the contact.
8. Upon receiving the presence stanza of type "subscribed" addressed
to the user, the user's server MUST first verify that the contact
is in the user's roster with either of the following states: (a)
subscription='none' and ask='subscribe' or (b)
subscription='from' and ask='subscribe'. If the contact is not
in the user's roster with either of those states, the user's
server MUST silently ignore the presence stanza of type
"subscribed" (i.e., it MUST NOT route it to the user, modify the
user's roster, or generate a roster push to the user's available
resources). If the contact is in the user's roster with either
of those states, the user's server (1) MUST deliver the presence
stanza of type "subscribed" from the contact to the user; (2)
MUST initiate a roster push to all of the user's available
resources that have requested the roster, containing an updated
roster item for the contact with the 'subscription' attribute set
to a value of "to"; and (3) MUST deliver the available presence
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stanza received from each of the contact's available resources to
each of the user's available resources:
<presence
to='user@example.com'
from='contact@example.org'
type='subscribed'/>
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@example.org'
subscription='to'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
<presence
from='contact@example.org/resource'
to='user@example.com/resource'/>
9. Upon receiving the presence stanza of type "subscribed", the user
SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "subscribe" to the contact or "denying" it by
sending a presence stanza of type "unsubscribe" to the contact;
this step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the user's server know that it MUST no longer send notification
of the subscription state change to the user (see Section 9.4).
From the perspective of the user, there now exists a subscription to
the contact; from the perspective of the contact, there now exists a
subscription from the user. (Note: If at this point the user sends
another subscription request to the contact, the user's server MUST
silently ignore that request.)
8.2.1 Alternate Flow: Contact Declines Subscription Request
The above activity flow represents the "happy path" related to the
user's subscription request to the contact. The main alternate flow
occurs if the contact refuses the user's subscription request.
1. If the contact wants to refuse the request, the contact's client
MUST send a presence stanza of type "unsubscribed" to the user
(instead of the presence stanza of type "subscribed" sent in Step
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6 of Section 8.2):
<presence to='user@example.com' type='unsubscribed'/>
2. As a result, the contact's server MUST route the presence stanza
of type "unsubscribed" to the user, first stamping the 'from'
address as the bare JID (<contact@example.org>) of the contact:
<presence
from='contact@example.org'
to='user@example.com'
type='unsubscribed'/>
Note: if the contact's server previously added the user to the
contact's roster for tracking purposes, it MUST remove the
relevant item at this time.
3. Upon receiving the presence stanza of type "unsubscribed"
addressed to the user, the user's server (1) MUST deliver that
presence stanza to the user and (2) MUST initiate a roster push
to all of the user's available resources that have requested the
roster, containing an updated roster item for the contact with
the 'subscription' attribute set to a value of "none" and with no
'ask' attribute:
<presence
from='contact@example.org'
to='user@example.com'
type='unsubscribed'/>
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@example.org'
subscription='none'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
4. Upon receiving the presence stanza of type "unsubscribed", the
user SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribe" to the contact or "denying" it by
sending a presence stanza of type "subscribe" to the contact;
this step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
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the user's server know that it MUST no longer send notification
of the subscription state change to the user (see Section 9.4).
As a result of this activity, the contact is now in the user's roster
with a subscription state of "none", whereas the user is not in the
contact's roster at all.
8.3 Creating a Mutual Subscription
The user and contact can build on the foregoing to create a mutual
subscription (i.e., a subscription of type "both"). The process is
defined below.
1. If the contact wants to create a mutual subscription, the contact
MUST send a subscription request to the user (subject to
configured preferences, the contact's client MAY send this
automatically):
<presence to='user@example.com' type='subscribe'/>
2. As a result, the contact's server (1) MUST initiate a roster push
to all available resources associated with the contact that have
requested the roster, with the user still in the 'from'
subscription state but with a pending 'to' subscription denoted
by the inclusion of the ask='subscribe' attribute in the roster
item; and (2) MUST route the presence stanza of type "subscribe"
to the user, first stamping the 'from' address as the bare JID
(<contact@example.org>) of the contact:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@example.com'
subscription='from'
ask='subscribe'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='contact@example.org'
to='user@example.com'
type='subscribe'/>
Note: If the contact's server receives a presence stanza of type
"error" from the user's server in response to the outgoing
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presence stanza of type "subscribe", it MUST revert the
subscription state from the new state ("From + Pending Out") to
the previous state ("From"), and MUST deliver the error stanza to
the contact.
3. Upon receiving the presence stanza of type "subscribe" addressed
to the user, the user's server must determine if there is at
least one available resource for which the user has requested the
roster. If so, the user's server MUST deliver the subscription
request to the user (if not, it MUST store the subscription
request offline for delivery when this condition is next met).
No matter when the subscription request is delivered, the user
must then decide whether or not to approve it (subject to
configured preferences, the user's client MAY approve or refuse
the subscription request without presenting it to the user).
Here we assume the "happy path" that the user approves the
subscription request (the alternate flow of declining the
subscription request is defined in Section 8.3.1). In this case,
the user's client MUST send a presence stanza of type
"subscribed" to the contact in order to approve the subscription
request.
<presence to='contact@example.org' type='subscribed'/>
4. As a result, the user's server (1) MUST initiate a roster push to
all of the user's available resources that have requested the
roster, containing a roster item for the contact with the
'subscription' attribute set to a value of "both"; (2) MUST route
the presence stanza of type "subscribed" to the contact, first
stamping the 'from' address as the bare JID (<user@example.com>)
of the user; and (3) MUST send available presence from each of
the user's available resources to the contact:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@example.org'
subscription='both'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
<presence
from='user@example.com'
to='contact@example.org'
type='subscribed'/>
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<presence
from='user@example.com/resource'
to='contact@example.org'/>
Note: If the user's server receives a presence stanza of type
"error" from the contact's server in response to the outgoing
presence stanza of type "subscribed", it MUST revert the
subscription state from the new state ("Both") to the previous
state ("To + Pending In"), and MUST deliver the error stanza to
the user.
5. Upon receiving the presence stanza of type "subscribed" addressed
to the contact, the contact's server MUST first verify that the
user is in the contact's roster with either of the following
states: (a) subscription='none' and ask='subscribe' or (b)
subscription='from' and ask='subscribe'. If the user is not in
the contact's roster with either of those states, the contact's
server MUST silently ignore the presence stanza of type
"subscribed" (i.e., it MUST NOT route it to the contact, modify
the contact's roster, or generate a roster push to the contact's
available resources). If the user is in the contact's roster
with either of those states, the contact's server (1) MUST
deliver the presence stanza of type "subscribed" from the user to
the contact; (2) MUST initiate a roster push to all available
resources associated with the contact that have requested the
roster, containing an updated roster item for the user with the
'subscription' attribute set to a value of "both"; and (3) MUST
deliver the available presence stanza received from each of the
user's available resources to each of the contact's available
resources:
<presence
from='user@example.com'
to='contact@example.org'
type='subscribed'/>
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@example.com'
subscription='both'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
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from='user@example.com/resource'
to='contact@example.org/resource'/>
6. Upon receiving the presence stanza of type "subscribed", the
contact SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "subscribe" to the user or "denying" it by sending
a presence stanza of type "unsubscribe" to the user; this step
does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the contact's server know that it MUST no longer send
notification of the subscription state change to the contact (see
Section 9.4).
The user and the contact now have a mutual subscription to each
other's presence -- i.e., the subscription is of type "both". The
user's server MUST now send the user's current presence information
to the contact. (Note: If at this point the user sends a
subscription request to the contact or the contact sends a
subscription request to the user, the sending user's server MUST
silently ignore that request and not route it to the intended
recipient.)
8.3.1 Alternate Flow: User Declines Subscription Request
The above activity flow represents the "happy path" related to the
contact's subscription request to the user. The main alternate flow
occurs if the user refuses the contact's subscription request.
1. If the user wants to refuse the request, the user's client MUST
send a presence stanza of type "unsubscribed" to the contact
(instead of the presence stanza of type "subscribed" sent in Step
3 of Section 8.3):
<presence to='contact@example.org' type='unsubscribed'/>
2. As a result, the user's server MUST route the presence stanza of
type "unsubscribed" to the contact, first stamping the 'from'
address as the bare JID (<user@example.com>) of the user:
<presence
from='user@example.com'
to='contact@example.org'
type='unsubscribed'/>
3. Upon receiving the presence stanza of type "unsubscribed"
addressed to the contact, the contact's server (1) MUST deliver
that presence stanza to the contact; and (2) MUST initiate a
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roster push to all available resources associated with the
contact that have requested the roster, containing an updated
roster item for the user with the 'subscription' attribute set to
a value of "from" and with no 'ask' attribute:
<presence
from='user@example.com'
to='contact@example.org'
type='unsubscribed'/>
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@example.com'
subscription='from'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
4. Upon receiving the presence stanza of type "unsubscribed", the
contact SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribe" to the user or "denying" it by
sending a presence stanza of type "subscribe" to the user; this
step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the contact's server know that it MUST no longer send
notification of the subscription state change to the contact (see
Section 9.4).
As a result of this activity, there has been no change in the
subscription state; i.e., the contact is in the user's roster with a
subscription state of "to" and the user is in the contact's roster
with a subscription state of "from".
8.4 Unsubscribing
At any time after subscribing to a contact's presence, a user MAY
unsubscribe. While the XML that the user sends to make this happen
is the same in all instances, the subsequent subscription state is
different depending on the subscription state obtaining when the
unsubscribe "command" is sent. Both possible scenarios are defined
below.
8.4.1 Case #1: Unsubscribing When Subscription is Not Mutual
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In the first case, the user has a subscription to the contact but the
contact does not have a subscription to the user (i.e., the
subscription is not yet mutual).
1. If the user wants to unsubscribe from the contact's presence, the
user MUST send a presence stanza of type "unsubscribe" to the
contact:
<presence to='contact@example.org' type='unsubscribe'/>
2. As a result, the user's server (1) MUST send a roster push to all
of the user's available resources that have requested the roster,
containing an updated roster item for the contact with the
'subscription' attribute set to a value of "none"; and (2) MUST
route the presence stanza of type "unsubscribe" to the contact,
first stamping the 'from' address as the bare JID
(<user@example.com>) of the user:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@example.org'
subscription='none'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
<presence
from='user@example.com'
to='contact@example.org'
type='unsubscribe'/>
3. Upon receiving the presence stanza of type "unsubscribe"
addressed to the contact, the contact's server (1) MUST initiate
a roster push to all available resources associated with the
contact that have requested the roster, containing an updated
roster item for the user with the 'subscription' attribute set to
a value of "none" (if the contact is offline, the contact's
server MUST modify the roster item and send that modified item
the next time the contact requests the roster); and (2) MUST
deliver the "unsubscribe" state change notification to the
contact:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
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jid='user@example.com'
subscription='none'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='user@example.com'
to='contact@example.org'
type='unsubscribe'/>
4. Upon receiving the presence stanza of type "unsubscribe", the
contact SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribed" to the user or "denying" it by
sending a presence stanza of type "subscribed" to the user; this
step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the contact's server know that it MUST no longer send
notification of the subscription state change to the contact (see
Section 9.4).
5. The contact's server then (1) MUST send a presence stanza of type
"unsubscribed" to the user; and (2) SHOULD send unavailable
presence from the contact to the user:
<presence
from='contact@example.org'
to='user@example.com'
type='unsubscribed'/>
<presence
from='contact@example.org'
to='user@example.com'
type='unavailable'/>
6. When the user's server receives a presence stanza of type
"unsubscribed" and/or unavailable presence, it MUST deliver them
to the user:
<presence
from='contact@example.org'
to='user@example.com'
type='unsubscribed'/>
<presence
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from='contact@example.org'
to='user@example.com'
type='unavailable'/>
7. Upon receiving the presence stanza of type "unsubscribed", the
user SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribe" to the contact or "denying" it by
sending a presence stanza of type "subscribe" to the contact;
this step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the user's server know that it MUST no longer send notification
of the subscription state change to the user (see Section 9.4).
8.4.2 Case #2: Unsubscribing When Subscription is Mutual
In the second case, the user has a subscription to the contact and
the contact also has a subscription to the user (i.e., the
subscription is mutual).
1. If the user wants to unsubscribe from the contact's presence, the
user MUST send a presence stanza of type "unsubscribe" to the
contact:
<presence to='contact@example.org' type='unsubscribe'/>
2. As a result, the user's server (1) MUST send a roster push to all
of the user's available resources that have requested the roster,
containing an updated roster item for the contact with the
'subscription' attribute set to a value of "from"; and (2) MUST
route the presence stanza of type "unsubscribe" to the contact,
first stamping the 'from' address as the bare JID
(<user@example.com>) of the user:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@example.org'
subscription='from'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
<presence
from='user@example.com'
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to='contact@example.org'
type='unsubscribe'/>
3. Upon receiving the presence stanza of type "unsubscribe"
addressed to the contact, the contact's server (1) MUST initiate
a roster push to all available resources associated with the
contact that have requested the roster, containing an updated
roster item for the user with the 'subscription' attribute set to
a value of "to" (if the contact is offline, the contact's server
MUST modify the roster item and send that modified item the next
time the contact requests the roster); and (2) MUST deliver the
"unsubscribe" state change notification to the contact:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@example.com'
subscription='to'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='user@example.com'
to='contact@example.org'
type='unsubscribe'/>
4. Upon receiving the presence stanza of type "unsubscribe", the
contact SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribed" to the user or "denying" it by
sending a presence stanza of type "subscribed" to the user; this
step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the contact's server know that it MUST no longer send
notification of the subscription state change to the contact (see
Section 9.4).
5. The contact's server then (1) MUST send a presence stanza of type
"unsubscribed" to the user; and (2) SHOULD send unavailable
presence from the contact to the user:
<presence
from='contact@example.org'
to='user@example.com'
type='unsubscribed'/>
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<presence
from='contact@example.org'
to='user@example.com'
type='unavailable'/>
6. When the user's server receives a presence stanza of type
"unsubscribed" and/or unavailable presence, it MUST deliver them
to the user:
<presence
from='contact@example.org'
to='user@example.com'
type='unsubscribed'/>
<presence
from='contact@example.org'
to='user@example.com'
type='unavailable'/>
7. Upon receiving the presence stanza of type "unsubscribed", the
user SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribe" to the contact or "denying" it by
sending a presence stanza of type "subscribe" to the contact;
this step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the user's server know that it MUST no longer send notification
of the subscription state change to the user (see Section 9.4).
Note: Obviously this does not result in removal of the roster item
from the user's roster, and the contact still has a subscription to
the user's presence. In order to both completely cancel a mutual
subscription and fully remove the roster item from the user's roster,
the user SHOULD update the roster item with subscription='remove' as
defined under Removing a Roster Item and Cancelling All Subscriptions
(Section 8.6).
8.5 Cancelling a Subscription
At any time after approving a subscription request from a user, a
contact MAY cancel that subscription. While the XML that the contact
sends to make this happen is the same in all instances, the
subsequent subscription state is different depending on the
subscription state obtaining when the cancellation was sent. Both
possible scenarios are defined below.
8.5.1 Case #1: Cancelling When Subscription is Not Mutual
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In the first case, the user has a subscription to the contact but the
contact does not have a subscription to the user (i.e., the
subscription is not yet mutual).
1. If the contact wants to cancel the user's subscription, the
contact MUST send a presence stanza of type "unsubscribed" to the
user:
<presence to='user@example.com' type='unsubscribed'/>
2. As a result, the contact's server (1) MUST send a roster push to
all of the contact's available resources that have requested the
roster, containing an updated roster item for the user with the
'subscription' attribute set to a value of "none"; (2) MUST route
the presence stanza of type "unsubscribed" to the user, first
stamping the 'from' address as the bare JID
(<contact@example.org>) of the contact; and (3) SHOULD send
unavailable presence from the contact to the user:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@example.com'
subscription='none'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='contact@example.org'
to='user@example.com'
type='unsubscribed'/>
<presence
from='contact@example.org'
to='user@example.com'
type='unavailable'/>
3. Upon receiving the presence stanza of type "unsubscribed"
addressed to the user, the user's server (1) MUST initiate a
roster push to all of the user's available resources that have
requested the roster, containing an updated roster item for the
contact with the 'subscription' attribute set to a value of
"none" (if the user is offline, the user's server MUST modify the
roster item and send that modified item the next time the user
requests the roster); (2) MUST deliver the "unsubscribed" state
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change notification to the user; and (3) MUST deliver the
unavailable presence to the user:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@example.org'
subscription='none'
name='MyContact'>
<group>MyBuddies</group>
</item>
</query>
</iq>
<presence
from='contact@example.org'
to='user@example.com'
type='unsubscribed'/>
<presence
from='contact@example.org'
to='user@example.com'
type='unavailable'/>
4. Upon receiving the presence stanza of type "unsubscribed", the
user SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribe" to the contact or "denying" it by
sending a presence stanza of type "subscribe" to the contact;
this step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the user's server know that it MUST no longer send notification
of the subscription state change to the user (see Section 9.4).
8.5.2 Case #2: Cancelling When Subscription is Mutual
In the second case, the user has a subscription to the contact and
the contact also has a subscription to the user (i.e., the
subscription is mutual).
1. If the contact wants to cancel the user's subscription, the
contact MUST send a presence stanza of type "unsubscribed" to the
user:
<presence to='user@example.com' type='unsubscribed'/>
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2. As a result, the contact's server (1) MUST send a roster push to
all of the contact's available resources that have requested the
roster, containing an updated roster item for the user with the
'subscription' attribute set to a value of "to"; (2) MUST route
the presence stanza of type "unsubscribed" to the user, first
stamping the 'from' address as the bare JID
(<contact@example.org>) of the contact; and (3) SHOULD send
unavailable presence from the contact to the user:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@example.com'
subscription='to'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='contact@example.org'
to='user@example.com'
type='unsubscribed'/>
<presence
from='contact@example.org'
to='user@example.com'
type='unavailable'/>
3. Upon receiving the presence stanza of type "unsubscribed"
addressed to the user, the user's server (1) MUST initiate a
roster push to all of the user's available resources that have
requested the roster, containing an updated roster item for the
contact with the 'subscription' attribute set to a value of
"from" (if the user is offline, the user's server MUST modify the
roster item and send that modified item the next time the user
requests the roster); and (2) MUST deliver the "unsubscribed"
state change notification to the user; and (3) MUST deliver the
unavailable presence to the user:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@example.org'
subscription='from'
name='MyContact'>
<group>MyBuddies</group>
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</item>
</query>
</iq>
<presence
from='contact@example.org'
to='user@example.com'
type='unsubscribed'/>
<presence
from='contact@example.org'
to='user@example.com'
type='unavailable'/>
4. Upon receiving the presence stanza of type "unsubscribed", the
user SHOULD acknowledge receipt of that subscription state
notification through either "affirming" it by sending a presence
stanza of type "unsubscribe" to the contact or "denying" it by
sending a presence stanza of type "subscribe" to the contact;
this step does not necessarily affect the subscription state (see
Subscription States (Section 9) for details), but instead lets
the user's server know that it MUST no longer send notification
of the subscription state change to the user (see Section 9.4).
Note: Obviously this does not result in removal of the roster item
from the contact's roster, and the contact still has a subscription
to the user's presence. In order to both completely cancel a mutual
subscription and fully remove the roster item from the contact's
roster, the contact should update the roster item with
subscription='remove' as defined under Removing a Roster Item and
Cancelling All Subscriptions (Section 8.6).
8.6 Removing a Roster Item and Cancelling All Subscriptions
Because there may be many steps involved in completely removing a
roster item and cancelling subscriptions in both directions, the
roster management protocol includes a "shortcut" method for doing so.
The process may be initiated no matter what the current subscription
state is by sending a roster set containing an item for the contact
with the 'subscription' attribute set to a value of "remove":
<iq type='set' id='remove1'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@example.org'
subscription='remove'/>
</query>
</iq>
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When the user removes a contact from his or her roster by setting the
'subscription' attribute to a value of "remove", the user's server
(1) MUST automatically cancel any existing presence subscription
between the user and the contact (both 'to' and 'from' as
appropriate); (2) MUST remove the roster item from the user's roster
and inform all of the user's available resources that have requested
the roster of the roster item removal; (3) MUST inform the resource
that initiated the removal of success; and (4) SHOULD send
unavailable presence to the contact:
<presence
from='user@example.com'
to='contact@example.org'
type='unsubscribe'/>
<presence
from='user@example.com'
to='contact@example.org'
type='unsubscribed'/>
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='contact@example.org'
subscription='remove'/>
</query>
</iq>
<iq type='result' id='remove1'/>
<presence
from='user@example.com'
to='contact@example.org'
type='unavailable'/>
Upon receiving the presence stanza of type "unsubscribe", the
contact's server (1) MUST initiate a roster push to all available
resources associated with the contact that have requested the roster,
containing an updated roster item for the user with the
'subscription' attribute set to a value of "to" (if the contact is
offline, the contact's server MUST modify the roster item and send
that modified item the next time the contact requests the roster);
and (2) MUST also deliver the "unsubscribe" state change notification
to the contact:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
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jid='user@example.com'
subscription='to'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='user@example.com'
to='contact@example.org'
type='unsubscribe'/>
Upon receiving the presence stanza of type "unsubscribed", the
contact's server (1) MUST initiate a roster push to all available
resources associated with the contact that have requested the roster,
containing an updated roster item for the user with the
'subscription' attribute set to a value of "none" (if the contact is
offline, the contact's server MUST modify the roster item and send
that modified item the next time the contact requests the roster);
and (2) MUST also deliver the "unsubscribe" state change notification
to the contact:
<iq type='set'>
<query xmlns='jabber:iq:roster'>
<item
jid='user@example.com'
subscription='none'
name='SomeUser'>
<group>SomeGroup</group>
</item>
</query>
</iq>
<presence
from='user@example.com'
to='contact@example.org'
type='unsubscribed'/>
Upon receiving the presence stanza of type "unavailable" addressed to
the contact, the contact's server MUST deliver the unavailable
presence to the user:
<presence
from='user@example.com'
to='contact@example.org'
type='unavailable'/>
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Note that when the user removes the contact from the user's roster,
the end state of the contact's roster is that the user is still in
the contact's roster with a subscription state of "none"; in order to
completely remove the roster item for the user, the contact needs to
also send a roster removal request.
9. Subscription States
This section provides detailed information about subscription states
and server handling of subscription-related presence stanzas (i.e.,
presence stanzas of type "subscribe", "subscribed", "unsubscribe",
and "unsubscribed").
9.1 Defined States
There are nine possible subscription states, which are described here
from the user's (not contact's) perspective:
1. "None" = contact and user are not subscribed to each other, and
neither has requested a subscription from the other
2. "None + Pending Out" = contact and user are not subscribed to
each other, and user has sent contact a subscription request but
contact has not replied yet
3. "None + Pending In" = contact and user are not subscribed to each
other, and contact has sent user a subscription request but user
has not replied yet (note: contact's server SHOULD NOT push or
deliver roster items in this state, but instead SHOULD wait until
contact has approved subscription request from user)
4. "None + Pending Out/In" = contact and user are not subscribed to
each other, contact has sent user a subscription request but user
has not replied yet, and user has sent contact a subscription
request but contact has not replied yet
5. "To" = user is subscribed to contact (one-way)
6. "To + Pending In" = user is subscribed to contact, and contact
has send user a subscription request but user has not replied yet
7. "From" = contact is subscribed to user (one-way)
8. "From + Pending Out" = contact is subscribed to user, and user
has sent contact a subscription request but contact has not
replied yet
9. "Both" = user and contact are subscribed to each other (two-way)
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9.2 Server Handling of Outbound Presence Subscription Stanzas
Outbound presence subscription stanzas enable the user to manage his
or her subscription to the contact (via the "subscribe" and
"unsubscribe" types), and to manage the contact's access to the
user's presence information (via the "subscribed" and "unsubscribed"
types).
Because it is possible for the user's server and the contact's server
to lose synchronization regarding subscription states, the user's
server MUST route all outbound presence stanzas of type "subscribe"
or "unsubscribe" to the contact so that the user is able to
resynchronize his or her subscription to the contact if needed.
The user's server SHOULD NOT route a presence stanza of type
"subscribed" or "unsubscribed" to the contact if the stanza does not
result in a subscription state change from the user's perspective,
and MUST NOT make a state change. If the stanza results in a
subscription state change, the user's server MUST route the stanza to
the contact and MUST make the appropriate state change. These rules
are summarized in the following tables.
Table 1: Recommended handling of outbound "subscribed" stanzas
+----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+----------------------------------------------------------------+
| "None" | no | no state change |
| "None + Pending Out" | no | no state change |
| "None + Pending In" | yes | "From" |
| "None + Pending Out/In" | yes | "From + Pending Out" |
| "To" | no | no state change |
| "To + Pending In" | yes | "Both" |
| "From" | no | no state change |
| "From + Pending Out" | no | no state change |
| "Both" | no | no state change |
+----------------------------------------------------------------+
Table 2: Recommended handling of outbound "unsubscribed" stanzas
+----------------------------------------------------------------+
| EXISTING STATE | ROUTE? | NEW STATE |
+----------------------------------------------------------------+
| "None" | no | no state change |
| "None + Pending Out" | no | no state change |
| "None + Pending In" | yes | "None" |
| "None + Pending Out/In" | yes | "None + Pending Out" |
| "To" | no | no state change |
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| "To + Pending In" | yes | "To" |
| "From" | yes | "None" |
| "From + Pending Out" | yes | "None + Pending Out" |
| "Both" | yes | "To" |
+----------------------------------------------------------------+
9.3 Server Handling of Inbound Presence Subscription Stanzas
Inbound presence subscription stanzas request a subscription-related
action from the user (via the "subscribe" type), inform the user of
subscription-related actions taken by the contact (via the
"unsubscribe" type), or enable the user to manage the contact's
access to the user's presence information (via the "subscribed" and
"unsubscribed" types).
When the user's server receives a subscription request for the user
from the contact (i.e., a presence stanza of type "subscribe"), it
MUST deliver that request to the user for approval if the user has
not already granted the contact access to the user's presence
information and if there is no pending inbound subscription request;
however, the user's server SHOULD NOT deliver the new request if
there is a pending inbound subscription request, since the previous
subscription request will have been recorded. If the user has
already granted the contact access to the user's presence
information, the user's server SHOULD auto-reply to an inbound
presense stanza of type "subscribe" from the contact by sending a
presence stanza of type "subscribed" to the contact on behalf of the
user; this rule enables the contact to resynchronize the subscription
state if needed. These rules are summarized in the following table.
Table 3: Recommended handling of inbound "subscribe" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | yes | "None + Pending In" |
| "None + Pending Out" | yes | "None + Pending Out/In" |
| "None + Pending In" | no | no state change |
| "None + Pending Out/In" | no | no state change |
| "To" | yes | "To + Pending In" |
| "To + Pending In" | no | no state change |
| "From" | no * | no state change |
| "From + Pending Out" | no * | no state change |
| "Both" | no * | no state change |
+------------------------------------------------------------------+
* Server SHOULD auto-reply with "subscribed" stanza
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When the user's server receives a presence stanza of type
"unsubscribe" for the user from the contact, if the stanza results in
a subscription state change from the user's perspective then the
user's server SHOULD auto-reply by sending a presence stanza of type
"unsubscribed" to the contact on behalf of the user, MUST deliver the
"unsubscribe" stanza to the user, and MUST change the state. If no
subscription state change results, the user's server SHOULD NOT
deliver the stanza and MUST NOT change the state. These rules are
summarized in the following table.
Table 4: Recommended handling of inbound "unsubscribe" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | no | no state change |
| "None + Pending Out" | no | no state change |
| "None + Pending In" | yes * | "None" |
| "None + Pending Out/In" | yes * | "None + Pending Out" |
| "To" | no | no state change |
| "To + Pending In" | yes * | "To" |
| "From" | yes * | "None" |
| "From + Pending Out" | yes * | "None + Pending Out |
| "Both" | yes * | "To" |
+------------------------------------------------------------------+
* Server SHOULD auto-reply with "unsubscribed" stanza
When the user's server receives a presence stanza of type
"subscribed" for the user from the contact, it MUST NOT deliver the
stanza to the user and MUST NOT change the subscription state if
there is no pending outbound request for access to the contact's
presence information. If there is a pending outbound request for
access to the contact's presence information and the inbound presence
stanza of type "subscribed" results in a subscription state change,
the user's server MUST deliver the stanza to the user and MUST change
the subscription state. If the user already has access to the
contact's presence information, the inbound presence stanza of type
"subscribed" does not result in a subscription state change;
therefore the user's server SHOULD NOT deliver the stanza to the user
and MUST NOT change the subscription state. These rules are
summarized in the following table.
Table 5: Recommended handling of inbound "subscribed" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
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| "None" | no | no state change |
| "None + Pending Out" | yes | "To" |
| "None + Pending In" | no | no state change |
| "None + Pending Out/In" | yes | "To + Pending In" |
| "To" | no | no state change |
| "To + Pending In" | no | no state change |
| "From" | no | no state change |
| "From + Pending Out" | yes | "Both" |
| "Both" | no | no state change |
+------------------------------------------------------------------+
When the user's server receives a presence stanza of type
"unsubscribed" for the user from the contact, it MUST deliver the
stanza to the user and MUST change the subscription state if there is
a pending outbound request for access to the contact's presence
information or if the user currently has access to the contact's
presence information. Otherwise, the user's server SHOULD NOT
deliver the stanza and MUST NOT change the subscription state. These
rules are summarized in the following table.
Table 6: Recommended handling of inbound "unsubscribed" stanzas
+------------------------------------------------------------------+
| EXISTING STATE | DELIVER? | NEW STATE |
+------------------------------------------------------------------+
| "None" | no | no state change |
| "None + Pending Out" | yes | "None" |
| "None + Pending In" | no | no state change |
| "None + Pending Out/In" | yes | "None + Pending In" |
| "To" | yes | "None" |
| "To + Pending In" | yes | "None + Pending In" |
| "From" | no | no state change |
| "From + Pending Out" | yes | "From" |
| "Both" | yes | "From" |
+------------------------------------------------------------------+
9.4 Server Delivery and Client Acknowledgement of Subscription State
Change Notifications
When a server receives an inbound presence stanza of type
"subscribe", "subscribed", "unsubscribe", or "unsubscribed" that
consists of a subscription state change request or notification, in
addition to sending the appropriate roster push (or updated roster
when the roster is next requested), it MUST deliver the request or
notification to the intended recipient at least once. A server MAY
require the recipient to acknowledge receipt of all state change
notifications (and MUST require acknowledgement in the case of
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subscription requests, i.e., presence stanzas of type "subscribe").
In order to require acknowledgement, a server SHOULD send the
notification to the recipient each time the recipient logs in, until
the recipient acknowledges receipt of the notification by "affirming"
or "denying" the notification, as shown in the following table:
Table 7: Acknowledgement of subscription state change notifications
+--------------------------------------------------+
| STANZA TYPE | ACCEPT | DENY |
+--------------------------------------------------+
| subscribe | subscribed | unsubscribed |
| subscribed | subscribe | unsubscribe |
| unsubscribe | unsubscribed | subscribed |
| unsubscribed | unsubscribe | subscribe |
+--------------------------------------------------+
Obviously, given the foregoing subscription state charts, some of the
acknowledgement stanzas will be routed to the contact and result in
subscription state changes, while others will not. However, any such
stanzas MUST result in the server's no longer sending the
subscription state notification to the user.
Because a user's server MUST automatically generate outbound presence
stanzas of type "unsubscribe" and "unsubscribed" upon receiving a
roster set with the 'subscription' attribute set to a value of
"remove" (see Removing a Roster Item and Cancelling All Subscriptions
(Section 8.6)), the server MUST treat a roster remove request as
equivalent to sending both of those presence stanzas for purposes of
determining whether to continue sending subscription state change
notifications of type "subscribe" or "subscribed" to the user.
10. Blocking Communication
Most instant messaging systems have found it necessary to implement
some method for users to block communications from particular other
users (this is also required by sections 5.1.5, 5.1.15, 5.3.2, and
5.4.10 of [IMP-REQS]). In XMPP this is done using the
'jabber:iq:privacy' namespace by managing one's privacy lists.
Server-side privacy lists enable successful completion of the
following use cases:
o Retrieving one's privacy lists.
o Adding, removing, and editing one's privacy lists.
o Setting, changing, or declining active lists.
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o Setting, changing, or declining the default list (i.e., the list
that is active by default).
o Allowing or blocking messages based on JID, group, or subscription
type (or globally).
o Allowing or blocking inbound presence notifications based on JID,
group, or subscription type (or globally).
o Allowing or blocking outbound presence notifications based on JID,
group, or subscription type (or globally).
o Allowing or blocking IQs based on JID, group, or subscription type
(or globally).
o Allowing or blocking all communications based on JID, group, or
subscription type (or globally).
Note: presence notifications do not include presence subscriptions,
only presence information that is broadcasted to entities that are
subscribed to a user's presence information. Thus this includes
presence stanzas with no 'type' attribute or of type='unavailable'
only.
10.1 Syntax and Semantics
A user MAY define one or more privacy lists, which are stored by the
user's server. Each <list/> element contains one or more rules in
the form of <item/> elements, and each <item/> element uses
attributes to define a privacy rule type, a specific value to which
the rules applies, the relevant action, and the place of the item in
the processing order.
The syntax is as follows:
<iq>
<query xmlns='jabber:iq:privacy'>
<list name='foo'>
<item
type='[jid|group|subscription]'
value='bar'
action='[allow|deny]'
order='unsignedInt'>
[<message/>]
[<presence-in/>]
[<presence-out/>]
[<iq/>]
</item>
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</list>
</query>
</iq>
If the type is "jid", then the 'value' attribute MUST contain a valid
Jabber ID. JIDs are matched in the following order: <user@domain/
resource>, then <user@domain>, then <domain/resource>, then <domain>.
If the value is <user@domain>, then any resource for that user@domain
matches. If the value is <domain/resource>, then only that resource
matches. If the value is <domain>, then any user@domain (or
subdomain) matches.
If the type is "group", then the 'value' attribute SHOULD contain the
name of a group in the user's roster. (If a client attempts to
update, create, or delete a list item with a group that is not in the
user's roster, the server SHOULD return to the client an
<item-not-found/> stanza error.)
If the type is "subscription", then the 'value' attribute MUST be one
of "both", "to", "from", or "none" as defined under Roster Syntax and
Semantics (Section 7.1).
If no 'type' attribute is included, the rule provides the
"fall-through" case.
The 'action' attribute MUST be included and its value MUST be either
"accept" or "deny".
The 'order' attribute MUST be included and its value MUST be a
non-negative integer that is unique among all items in the list. (If
a client attempts to create or update a list with non-unique order
values, the server MUST return to the client a <bad-request/> stanza
error.)
The <item/> element MAY contain one or more child elements that
enable an entity to specify more granular control over which kinds of
stanzas are to be blocked (i.e., rather than blocking all stanzas).
The allowable child elements are:
o <message/> -- blocks incoming message stanzas
o <iq/> -- blocks incoming IQ stanzas
o <presence-in/> -- blocks incoming presence notifications
o <presence-out/> -- blocks outgoing presence notifications
Within the 'jabber:iq:privacy' namespace, the <query/> child of a
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client-generated IQ stanza of type "set" MUST NOT include more than
one child element (i.e., the stanza must contain only one <active/>
element, one <default/> element, or one <list/> element); if a client
violates this rule, the server MUST return to the client a
<bad-request/> stanza error.
When a client adds or updates a privacy list, the <list/> element
SHOULD contain at least one <item/> child element; when a client
removes a privacy list, the <list/> element SHOULD contain no <item/>
child element.
When a client updates a privacy list, it must include all of the
desired items (i.e., not a "delta").
10.2 Business Rules
1. If there is an active list set for a session, it affects only
the session for which it is activated, and only for the duration
of the session. The server MUST apply the active list only and
MUST NOT apply the default list.
2. The default list applies to the user as a whole, and is
processed if there is no active list set for the target session/
resource to which a stanza is addressed, or if there are no
current sessions for the user.
3. If there is no active list set for a session (or there are no
current sessions for the user), and there is no default list,
then all stanzas SHOULD BE accepted or appropriately processed
by the server on behalf of the user.
4. Privacy lists MUST be the first rule applied by a server,
superseding (1) the routing and delivery rules specified in
Server Rules for Handling XML Stanzas (Section 11), and (2) the
handling of subscription-related presence stanzas (and
corresponding generation of roster pushes) specified in
Integration of Roster Items and Presence Subscriptions (Section
8).
5. The order in which privacy list items are processed by the
server is important. List items MUST be processed in ascending
order determined by the integer values of the 'order' attribute
for each <item/>.
6. As soon as a stanza is matched against a privacy list, the
server SHOULD appropriately handle the stanza and cease
processing.
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7. If no fall-through item is provided in a list, the fall-through
action is assumed to be "accept".
8. If a user updates the definition for an active list, subsequent
processing based on that active list MUST use the updated
definition (for all resources to which that active list
currently applies).
9. If a user modifies an active list by adding, modifying, or
deleting an item with the result that subsequent outbound
presence notifications will be blocked to certain subscribed
contacts, the server MUST also send unavailable presence from
the user to the affected contacts.
10. If a user modifies an active list by adding, modifying, or
deleting an item with the result that subsequent outbound
presence notifications will no longer be blocked to certain
subscribed contacts, the server MUST also send last available
presence from the user to the affected contacts.
11. If a change to the subscription state or roster group of a
roster item defined in an active or default list occurs during a
user's session, subsequent processing based on that list MUST
take into account the changed state or group (for all resources
to which that list currently applies).
10.3 Retrieving One's Privacy Lists
Example: Client requests names of privacy lists from server:
<iq from='romeo@example.org/orchard' type='get' id='getlist1'>
<query xmlns='jabber:iq:privacy'/>
</iq>
Example: Server sends names of privacy lists to client, preceded by
active list and default list:
<iq type='result' id='getlist1' to='romeo@example.net/orchard'>
<query xmlns='jabber:iq:privacy'>
<active name='private'/>
<default name='public'/>
<list name='public'/>
<list name='private'/>
<list name='special'/>
</query>
</iq>
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Example: Client requests a privacy list from server:
<iq from='romeo@example.org/orchard' type='get' id='getlist2'>
<query xmlns='jabber:iq:privacy'>
<list name='public'/>
</query>
</iq>
Example: Server sends a privacy list to client:
<iq type='result' id='getlist2' to='romeo@example.net/orchard'>
<query xmlns='jabber:iq:privacy'>
<list name='public'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='1'/>
<item action='allow' order='2'/>
</list>
</query>
</iq>
Example: Client requests another privacy list from server:
<iq from='romeo@example.org/orchard' type='get' id='getlist3'>
<query xmlns='jabber:iq:privacy'>
<list name='private'/>
</query>
</iq>
Example: Server sends another privacy list to client:
<iq type='result' id='getlist3' to='romeo@example.net/orchard'>
<query xmlns='jabber:iq:privacy'>
<list name='private'>
<item type='subscription'
value='both'
action='allow'
order='10'/>
<item action='deny' order='15'/>
</list>
</query>
</iq>
Example: Client requests yet another privacy list from server:
<iq from='romeo@example.org/orchard' type='get' id='getlist4'>
<query xmlns='jabber:iq:privacy'>
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<list name='special'/>
</query>
</iq>
Example: Server sends yet another privacy list to client:
<iq type='result' id='getlist4' to='romeo@example.net/orchard'>
<query xmlns='jabber:iq:privacy'>
<list name='special'>
<item type='jid'
value='juliet@example.com'
action='allow'
order='6'/>
<item type='jid'
value='benvolio@example.org'
action='allow'
order='7'/>
<item type='jid'
value='mercutio@example.org'
action='allow'
order='42'/>
<item action='deny' order='666'/>
</list>
</query>
</iq>
In this example, the user has three lists: (1) 'public', which allows
communications from everyone except one specific entity (this is the
default list); (2) 'private', which allows communications only with
contacts who have a bidirectional subscription with the user (this is
the active list); and (3) 'special', which allows communications only
with three specific entities.
If the user attempts to retrieve a list but a list by that name does
not exist, the server MUST return an <item-not-found/> stanza error
to the user:
Example: Client attempts to retrieve non-existent list:
<iq to='romeo@example.org/orchard' type='error' id='getlist5'>
<query xmlns='jabber:iq:privacy'>
<list name='The Empty Set'/>
</query>
<error type='cancel'>
<item-not-found
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
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The user is allowed to retrieve only one list at a time. If the user
attempts to retrieve more than one list in the same request, the
server MUST return a <bad request/> stanza error to the user:
Example: Client attempts to retrieve more than one list:
<iq to='romeo@example.org/orchard' type='error' id='getlist6'>
<query xmlns='jabber:iq:privacy'>
<list name='public'/>
<list name='private'/>
<list name='special'/>
</query>
<error type='modify'>
<bad-request
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
10.4 Managing Active Lists
In order to set or change the active list currently being applied by
the server, the user MUST send an IQ stanza of type "set" with a
<query/> element qualified by the 'jabber:iq:privacy' namespace that
contains an empty <active/> child element possessing a 'name'
attribute whose value is set to the desired list name.
Example: Client requests change of active list:
<iq from='romeo@example.org/orchard' type='set' id='active1'>
<query xmlns='jabber:iq:privacy'>
<active name='special'/>
</query>
</iq>
The server MUST activate and apply the requested list before sending
the result back to the client.
Example: Server acknowledges success of active list change:
<iq type='result' id='active1' to='romeo@example.org/orchard'/>
If the user attempts to set an active list but a list by that name
does not exist, the server MUST return an <item-not-found/> stanza
error to the user:
Example: Client attempts to set a non-existent list as active:
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<iq to='romeo@example.org/orchard' type='error' id='active2'>
<query xmlns='jabber:iq:privacy'>
<active name='The Empty Set'/>
</query>
<error type='cancel'>
<item-not-found
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
In order to decline the use of any active list, the user MUST send an
empty <active/> element with no name.
Example: Client declines the use of active lists:
<iq from='romeo@example.org/orchard' type='set' id='active2'>
<query xmlns='jabber:iq:privacy'>
<active/>
</query>
</iq>
10.5 Managing the Default List
In order to change its default list, the user MUST send an IQ stanza
of type "set" with a <query/> element qualified by the
'jabber:iq:privacy' namespace that contains an empty <default/> child
element possessing a 'name' attribute whose value is set to the
desired list name.
Example: Client requests change of default list:
<iq from='romeo@example.org/orchard' type='set' id='default1'>
<query xmlns='jabber:iq:privacy'>
<default name='special'/>
</query>
</iq>
Example: Server acknowledges success of default list change:
<iq type='result' id='default1' to='romeo@example.org/orchard'/>
If the user attempts to set a default list but a list by that name
does not exist, the server MUST return an <item-not-found/> stanza
error to the user:
Example: Client attempts to set a non-existent list as default:
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<iq to='romeo@example.org/orchard' type='error' id='default2'>
<query xmlns='jabber:iq:privacy'>
<default name='The Empty Set'/>
</query>
<error type='cancel'>
<item-not-found
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
In order to decline the use of a default list (i.e., to use the
domain's stanza routing rules at all times), the user MUST send an
empty <default/> element with no name.
Example: Client declines the use of the default list:
<iq from='romeo@example.org/orchard' type='set' id='default2'>
<query xmlns='jabber:iq:privacy'>
<default/>
</query>
</iq>
10.6 Editing a Privacy List
In order to edit a privacy list, the user MUST send an IQ stanza of
type "set" with a <query/> element qualified by the
'jabber:iq:privacy' namespace that contains one <list/> child element
possessing a 'name' attribute whose value is set to the list name the
user would like to edit. The <list/> element MUST contain one or
more <item/> elements, which specify the user's desired changes to
the list by including all elements in the list (not the "delta").
Example: Client edits a privacy list:
<iq from='romeo@example.org/orchard' type='set' id='edit1'>
<query xmlns='jabber:iq:privacy'>
<list name='public'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='3'/>
<item type='jid'
value='paris@example.org'
action='deny'
order='5'/>
<item action='allow' order='68'/>
</list>
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</query>
</iq>
Example: Server acknowledges success of list edit:
<iq type='result' id='edit1' to='juliet@example.com/balcony'/>
Note: The value of the 'order' attribute for any given item is not
fixed. Thus in the foregoing example if the user would like to add 4
items between the "tybalt@example.com" item and the
"paris@example.org" item, the user's client MUST renumber the
relevant items before submitting the list to the server.
10.7 Adding a New Privacy List
The same protocol used to edit an existing list is used to create a
new list. If the list name matches that of an existing list, the
request to add a new list will overwrite the old one.
10.8 Removing a Privacy List
In order to remove a privacy list, the user MUST send an IQ stanza of
type "set" with a <query/> element qualified by the
'jabber:iq:privacy' namespace that contains one empty <list/> child
element possessing a 'name' attribute whose value is set to the list
name the user would like to remove.
Example: Client removes a privacy list:
<iq from='romeo@example.org/orchard' type='set' id='remove1'>
<query xmlns='jabber:iq:privacy'>
<list name='private'/>
</query>
</iq>
Example: Server acknowledges success of list removal:
<iq type='result' id='remove1' to='juliet@example.com/balcony'/>
If a user attempts to remove an active list or the default list, the
server MUST return a <conflict/> stanza error to the user. The user
MUST first set another list to active or default before removing it.
If the user attempts to remove a list but a list by that name does
not exist, the server MUST return an <item-not-found/> stanza error
to the user:
If the user attempts to remove more than one list in the same
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request, the server MUST return a <bad request/> stanza error to the
user.
10.9 Blocking Messages
Server-side privacy lists enable a user to block incoming messages
from other users based on the other user's JID, roster group, or
subscription status (or globally). The following examples illustrate
the protocol.
Example: User blocks based on JID:
<iq from='romeo@example.org/orchard' type='set' id='msg1'>
<query xmlns='jabber:iq:privacy'>
<list name='message-jid-example'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='3'>
<message/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive messages from the user with the specified JID.
Example: User blocks based on roster group:
<iq from='romeo@example.org/orchard' type='set' id='msg2'>
<query xmlns='jabber:iq:privacy'>
<list name='message-group-example'>
<item type='group'
value='Enemies'
action='deny'
order='4'>
<message/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive messages from any users in the specified roster
group.
Example: User blocks based on subscription type:
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<iq from='romeo@example.org/orchard' type='set' id='msg3'>
<query xmlns='jabber:iq:privacy'>
<list name='message-sub-example'>
<item type='subscription'
value='none'
action='deny'
order='5'>
<message/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive messages from any users with the specified
subscription type.
Example: User blocks globally:
<iq from='romeo@example.org/orchard' type='set' id='msg4'>
<query xmlns='jabber:iq:privacy'>
<list name='message-global-example'>
<item action='deny' order='6'>
<message/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive messages from any other users.
10.10 Blocking Inbound Presence Notifications
Server-side privacy lists enable a user to block incoming presence
notifications from other users based on the other user's JID, roster
group, or subscription status (or globally). The following examples
illustrate the protocol.
Note: presence notifications do not include presence subscriptions,
only presence information that is broadcasted to the user because the
user is currently subscribed to a contact's presence information.
Thus this includes presence stanzas with no 'type' attribute or of
type='unavailable' only.
Example: User blocks based on JID:
<iq from='romeo@example.org/orchard' type='set' id='presin1'>
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<query xmlns='jabber:iq:privacy'>
<list name='presin-jid-example'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='7'>
<presence-in/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive presence notifications from the user with the
specified JID.
Example: User blocks based on roster group:
<iq from='romeo@example.org/orchard' type='set' id='presin2'>
<query xmlns='jabber:iq:privacy'>
<list name='presin-group-example'>
<item type='group'
value='Enemies'
action='deny'
order='8'>
<presence-in/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive presence notifications from any users in the
specified roster group.
Example: User blocks based on subscription type:
<iq from='romeo@example.org/orchard' type='set' id='presin3'>
<query xmlns='jabber:iq:privacy'>
<list name='presin-sub-example'>
<item type='subscription'
value='to'
action='deny'
order='9'>
<presence-in/>
</item>
</list>
</query>
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</iq>
As a result of creating and applying the foregoing list, the user
will not receive presence notifications from any users with the
specified subscription type.
Example: User blocks globally:
<iq from='romeo@example.org/orchard' type='set' id='presin4'>
<query xmlns='jabber:iq:privacy'>
<list name='presin-global-example'>
<item action='deny' order='11'>
<presence-in/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive presence notifications from any other users.
10.11 Blocking Outbound Presence Notifications
Server-side privacy lists enable a user to block outgoing presence
notifications to other users based on the other user's JID, roster
group, or subscription status (or globally). The following examples
illustrate the protocol.
Note: presence notifications do not include presence subscriptions,
only presence information that is broadcasted to contacts because
those contacts are currently subscribed to the user's presence
information. Thus this includes presence stanzas with no 'type'
attribute or of type='unavailable' only.
Example: User blocks based on JID:
<iq from='romeo@example.org/orchard' type='set' id='presout1'>
<query xmlns='jabber:iq:privacy'>
<list name='presout-jid-example'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='13'>
<presence-out/>
</item>
</list>
</query>
</iq>
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As a result of creating and applying the foregoing list, the user
will not send presence notifications to the user with the specified
JID.
Example: User blocks based on roster group:
<iq from='romeo@example.org/orchard' type='set' id='presout2'>
<query xmlns='jabber:iq:privacy'>
<list name='presout-group-example'>
<item type='group'
value='Enemies'
action='deny'
order='15'>
<presence-out/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not send presence notifications to any users in the specified
roster group.
Example: User blocks based on subscription type:
<iq from='romeo@example.org/orchard' type='set' id='presout3'>
<query xmlns='jabber:iq:privacy'>
<list name='presout-sub-example'>
<item type='subscription'
value='from'
action='deny'
order='17'>
<presence-out/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not send presence notifications to any users with the specified
subscription type.
Example: User blocks globally:
<iq from='romeo@example.org/orchard' type='set' id='presout4'>
<query xmlns='jabber:iq:privacy'>
<list name='presout-global-example'>
<item action='deny' order='23'>
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<presence-out/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not send presence notifications to any other users.
10.12 Blocking IQs
Server-side privacy lists enable a user to block incoming IQ stanzas
from other users based on the other user's JID, roster group, or
subscription status (or globally). The following examples illustrate
the protocol.
Example: User blocks based on JID:
<iq from='romeo@example.org/orchard' type='set' id='iq1'>
<query xmlns='jabber:iq:privacy'>
<list name='iq-jid-example'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='29'>
<iq/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive IQ stanzas from the user with the specified JID.
Example: User blocks based on roster group:
<iq from='romeo@example.org/orchard' type='set' id='iq2'>
<query xmlns='jabber:iq:privacy'>
<list name='iq-group-example'>
<item type='group'
value='Enemies'
action='deny'
order='31'>
<iq/>
</item>
</list>
</query>
</iq>
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As a result of creating and applying the foregoing list, the user
will not receive IQ stanzas from any users in the specified roster
group.
Example: User blocks based on subscription type:
<iq from='romeo@example.org/orchard' type='set' id='iq3'>
<query xmlns='jabber:iq:privacy'>
<list name='iq-sub-example'>
<item type='subscription'
value='none'
action='deny'
order='17'>
<iq/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive IQ stanzas from any users with the specified
subscription type.
Example: User blocks globally:
<iq from='romeo@example.org/orchard' type='set' id='iq4'>
<query xmlns='jabber:iq:privacy'>
<list name='iq-global-example'>
<item action='deny' order='1'>
<iq/>
</item>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive IQ stanzas from any other users.
10.13 Blocking All Communication
Server-side privacy lists enable a user to block all stanzas from and
to other users based on the other user's JID, roster group, or
subscription status (or globally). Note that this includes
subscription-related presence stanzas, which are excluded by Blocking
Inbound Presence Notifications (Section 10.10). The following
examples illustrate the protocol.
Example: User blocks based on JID:
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<iq from='romeo@example.org/orchard' type='set' id='all1'>
<query xmlns='jabber:iq:privacy'>
<list name='all-jid-example'>
<item type='jid'
value='tybalt@example.com'
action='deny'
order='23'/>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive any communications from, nor send any stanzas to,
the user with the specified JID.
Example: User blocks based on roster group:
<iq from='romeo@example.org/orchard' type='set' id='all2'>
<query xmlns='jabber:iq:privacy'>
<list name='all-group-example'>
<item type='group'
value='Enemies'
action='deny'
order='13'/>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive any communications from, nor send any stanzas to,
any users in the specified roster group.
Example: User blocks based on subscription type:
<iq from='romeo@example.org/orchard' type='set' id='all3'>
<query xmlns='jabber:iq:privacy'>
<list name='all-sub-example'>
<item type='subscription'
value='none'
action='deny'
order='11'/>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive any communications from, nor send any stanzas to,
any users with the specified subscription type.
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Example: User blocks globally:
<iq from='romeo@example.org/orchard' type='set' id='all4'>
<query xmlns='jabber:iq:privacy'>
<list name='all-global-example'>
<item action='deny' order='7'/>
</list>
</query>
</iq>
As a result of creating and applying the foregoing list, the user
will not receive any communications from, nor send any stanzas to,
any other users.
10.14 Blocked Entity Attempts to Communicate with User
If a blocked entity attempts to send message or presence stanzas to
the user, the user's server SHOULD silently drop the stanza and MUST
NOT return an error to the sending entity.
If a blocked entity attempts to send an IQ stanza of type "get" or
"set" to the user, the user's server MUST return to the sending
entity a <feature-not-implemented/> stanza error, since this is the
standard error code sent from a client that does not understand the
namespace of an IQ get or set. IQ stanzas of other types SHOULD be
silently dropped by the server.
Example: Blocked entity attempts to send IQ get:
<iq type='get'
to='romeo@example.net'
from='tybalt@example.com/pda'
id='probing1'>
<query xmlns='jabber:iq:version'/>
</iq>
Example: Server returns error to blocked entity:
<iq type='error'
from='romeo@example.net'
to='tybalt@example.com/pda'
id='probing1'>
<query xmlns='jabber:iq:version'/>
<error type='cancel'>
<feature-not-implemented
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
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10.15 Higher-Level Heuristics
When building a representation of a higher-level privacy heuristic, a
client SHOULD use the simplest possible representation.
For example, the heuristic "block all communications with any user
not in my roster" could be constructed in any of the following ways:
o allow communications from all JIDs in my roster (i.e., listing
each JID as a separate list item), but block communications with
everyone else
o allow communications from any user who is in one of the groups
that make up my roster (i.e., listing each group as a separate
list item), but block communications from everyone else
o allow communications from any user with whom I have a subscription
of 'both' or 'to' or 'from' (i.e., listing each subscription value
separately), but block communications from everyone else
o block communications from anyone whose subscription state is
'none'
The final representation is the simplest and SHOULD be used; here is
the XML that would be sent in this case:
<iq type='set' id='heuristic1'>
<query xmlns='jabber:iq:privacy'>
<list name='heuristic-example'>
<item type='subscription'
value='none'
action='deny'
order='437'/>
</list>
</query>
</iq>
11. Server Rules for Handling XML Stanzas
Basic routing and delivery rules for servers are defined in
[XMPP-CORE]. This section defines additional rules for
XMPP-compliant instant messaging and presence servers.
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute of a stanza matches the hostname of the server
itself and the JID contained in the 'to' attribute is of the form
<user@example.com> or <user@example.com/resource>, the server MUST
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first apply any privacy rules (Section 10) that are in force. If
privacy rules allow the stanza, it SHOULD be routed or delivered to
the intended recipient of the stanza as represented by the JID
contained in the 'to' attribute. The following additional rules
apply to instant messaging and presence applications, over and above
those defined in [XMPP-CORE]:
1. If the JID is of the form <user@domain/resource> and an active
resource matches the full JID, the recipient's server MUST
deliver the stanza to that resource.
2. If the JID is of the form <user@domain/resource> and no active
resource matches the full JID, the recipient's server (a) SHOULD
silently ignore the stanza (i.e., neither deliver it nor return
an error) if it is a presence stanza, (b) MUST return a
<service-unavailable/> stanza error to the sender if it is an IQ
stanza, and (c) SHOULD treat the stanza as if it were addressed
to <user@domain> if it is a message stanza.
3. If the JID is of the form <user@domain> and there is at least one
available resource available for the user, the recipient's server
MUST follow these rules:
1. For message stanzas, the server SHOULD deliver the stanza to
the highest-priority available resource (if the resource did
not provide a value for the <priority/> element, the server
SHOULD consider it to have provided a value of zero). If two
available resources have the same priority, the server MAY
use some other rule (e.g., most recent connect time, most
recent activity time, or highest availability as determined
by some hierarchy of <show/> values) to choose between them.
However, the server MUST NOT deliver the stanza to an
available resource with a negative priority; if the only
available resource has a negative priority, the server SHOULD
handle the message as if there were no available resources
(defined below). In addition, the server MUST NOT rewrite
the 'to' attribute (i.e., it MUST leave it as <user@domain>
rather than change it to <user@domain/resource>).
2. For presence stanzas other than those of type "probe", the
server MUST deliver the stanza to all available resources;
for presence probes, the server SHOULD reply based on the
rules defined in Client and Server Presence Responsibilities
(Section 5.1). In addition, the server MUST NOT rewrite the
'to' attribute (i.e., it MUST leave it as <user@domain>
rather than change it to <user@domain/resource>).
3. For IQ stanzas, the server itself MUST reply on behalf of the
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user with either an IQ result or an IQ error, and MUST NOT
deliver the IQ stanza to any of the available resources.
Specifically, if the semantics of the qualifying namespace
define a reply that the server can provide, the server MUST
reply to the stanza on behalf of the user; if not, the server
MUST reply with a <service-unavailable/> stanza error.
4. If the JID is of the form <user@domain> and there are no
available resources associated with the user, how the stanza is
handled depends on the stanza type:
1. For presence stanzas of type "subscribe", the server MUST
maintain a record of the stanza and deliver the request when
the user next creates an available resource, until the user
either approves or denies it.
2. For all other presence stanzas, the server SHOULD silently
ignore the stanza by not storing it for later delivery or
replying to it on behalf of the user.
3. For message stanzas, the server MAY choose to store the
stanza on behalf of the user and deliver it when the user
next becomes available. However, if offline message storage
is not enabled, the server MUST return to the sender a
<service-unavailable/> stanza error. (Note: offline message
storage is not defined in XMPP since it strictly is a matter
of implementation and service provisioning.)
4. For IQ stanzas, the server itself MUST reply on behalf of the
user with either an IQ result or an IQ error. Specifically,
if the semantics of the qualifying namespace define a reply
that the server can provide, the server MUST reply to the
stanza on behalf of the user; if not, the server MUST reply
with a <service-unavailable/> stanza error.
12. IM and Presence Compliance Requirements
This section summarizes the specific aspects of the Extensible
Messaging and Presence Protocol that MUST be supported by instant
messaging and presence servers and clients in order to be considered
compliant implementations. All such applications MUST comply with
the requirements specified in [XMPP-CORE]. The text in this section
specifies additional compliance requirements for instant messaging
and presence servers and clients; note well that the requirements
described here supplement but do not supersede the core requirements.
Note also that a server or client may support only presence or
instant messaging, and is not required to support both if only a
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presence service or an instant messaging service is desired.
12.1 Servers
In addition to core server compliance requirements, an instant
messaging and presence server MUST additionally support the following
protocols:
o All server-related instant messaging and presence syntax and
semantics defined in this document, including presence broadcast
on behalf of clients, presence subscriptions, roster storage and
manipulation, privacy rules, and IM-specific routing and delivery
rules
12.2 Clients
In addition to core client compliance requirements, an instant
messaging and presence client MUST additionally support the following
protocols:
o Generation and handling of the IM-specific semantics of XML
stanzas as defined by the XML schemas, including the 'type'
attribute of message and presence stanzas as well as their child
elements
o All client-related instant messaging syntax and semantics defined
in this document, including presence subscriptions, roster
management, and privacy rules
o End-to-end object encryption as defined in XMPP e2e [XMPP-E2E]
13. Internationalization Considerations
For internationalization considerations, refer to the relevant
section of [XMPP-CORE].
14. Security Considerations
Core security considerations for XMPP are defined in the relevant
section of [XMPP-CORE].
Additional considerations that apply only to instant messaging and
presence applications of XMPP are defined in several places within
this memo; specifically:
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o When a server processes a stanza of any kind whose intended
recipient is a user associated with one of the server's hostnames,
the server MUST first apply any privacy rules (Section 10) that
are in force (see Server Rules for Handling XML Stanzas (Section
11)).
o When a server processes an inbound presence stanza of type "probe"
whose intended recipient is a user associated with one of the
server's hostnames, the server MUST NOT reveal the user's presence
information if the sender is a user who is not authorized to
receive that information as determined by presence subscriptions
(see Client and Server Presence Responsibilities (Section 5.1)).
o When a server processes an outbound presence stanza with no type
or of type "unavailable", it MUST follow the rules defined under
Client and Server Presence Responsibilities (Section 5.1) in order
to ensure that such presence information is not broadcasted to
entities that are not authorized to know such information.
15. IANA Considerations
For a number of related IANA considerations, refer to the relevant
section of [XMPP-CORE].
15.1 XML Namespace Name for Session Data
A URN sub-namespace for session-related data in the Extensible
Messaging and Presence Protocol (XMPP) is defined as follows. (This
namespace name adheres to the format defined in The IETF XML Registry
[XML-REG].)
URI: urn:ietf:params:xml:ns:xmpp-session
Specification: XXXX
Description: This is the XML namespace name for session-related data
in the Extensible Messaging and Presence Protocol (XMPP) as
defined by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
15.2 Instant Messaging SRV Protocol Label Registration
Address Resolution for Instant Messaging and Presence [IMP-SRV]
defines an Instant Messaging SRV Protocol Label registry for
protocols that can provide services that conform to the "_im" SRV
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Service label. Because XMPP is one such protocol, the IANA registers
the "_xmpp" protocol label in the appropriate registry, as follows:
Protocol label: _xmpp
Specification: XXXX
Description: Instant messaging protocol label for the Extensible
Messaging and Presence Protocol (XMPP) as defined by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
15.3 Presence SRV Protocol Label Registration
Address Resolution for Instant Messaging and Presence [IMP-SRV]
defines a Presence SRV Protocol Label registry for protocols that can
provide services that conform to the "_pres" SRV Service label.
Because XMPP is one such protocol, the IANA registers the "_xmpp"
protocol label in the appropriate registry, as follows:
Protocol label: _xmpp
Specification: XXXX
Description: Presence protocol label for the Extensible Messaging and
Presence Protocol (XMPP) as defined by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
Normative References
[IMP-REQS]
Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging /
Presence Protocol Requirements", RFC 2779, February 2000.
[IMP-SRV] Peterson, J., "Address Resolution for Instant Messaging
and Presence", draft-ietf-impp-srv-04 (work in progress),
October 2003.
[TERMS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
"Extensible Markup Language (XML) 1.0 (2nd ed)", W3C
REC-xml, October 2000, <http://www.w3.org/TR/REC-xml>.
[XML-NAMES]
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Bray, T., Hollander, D. and A. Layman, "Namespaces in
XML", W3C REC-xml-names, January 1999, <http://www.w3.org/
TR/REC-xml-names>.
[XMPP-CORE]
Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", draft-ietf-xmpp-core-20 (work in
progress), November 2003.
[XMPP-E2E]
Saint-Andre, P., "End-to-End Object Encryption in the
Extensible Messaging and Presence Protocol (XMPP)",
draft-ietf-xmpp-e2e-05 (work in progress), August 2003.
Informative References
[JSF] Jabber Software Foundation, "Jabber Software Foundation",
<http://www.jabber.org/>.
[IMP-MODEL]
Day, M., Rosenberg, J. and H. Sugano, "A Model for
Presence and Instant Messaging", RFC 2778, February 2000.
[VCARD] Dawson, F. and T. Howes, "vCard MIME Directory Profile",
RFC 2426, September 1998.
[XML-REG] Mealling, M., "The IETF XML Registry",
draft-mealling-iana-xmlns-registry-05 (work in progress),
June 2003.
Author's Address
Peter Saint-Andre
Jabber Software Foundation
EMail: stpeter@jabber.org
Appendix A. vCards
Sections 3.1.3 and 4.1.4 of [IMP-REQS] require that it be possible to
retrieve out-of-band contact information for other users (e.g.,
telephone number or email address). An XML representation of the
vCard specification defined in RFC 2426 [VCARD] is in common use
within the Jabber community to provide such information but is out of
scope for XMPP (documentation of this protocol is contained in
"JEP-0054: vcard-temp", published by the Jabber Software Foundation
[JSF]).
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Appendix B. XML Schemas
The following XML schemas are descriptive, not normative. For
schemas defining the core features of XMPP, refer to [XMPP-CORE].
B.1 jabber:client
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
xmlns:xml='http://www.w3.org/XML/1998/namespace'
targetNamespace='jabber:client'
xmlns='jabber:client'
elementFormDefault='qualified'>
<xs:import namespace='http://www.w3.org/XML/1998/namespace'
schemaLocation='http://www.w3.org/2001/xml.xsd'/>
<xs:element name='message'>
<xs:complexType>
<xs:sequence>
<xs:element ref='subject'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='body'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='thread'
minOccurs='0'
maxOccurs='1'/>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='from'
type='xs:string'
use='optional'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute name='to'
type='xs:string'
use='optional'/>
<xs:attribute name='type' use='optional' default='normal'>
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<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='chat'/>
<xs:enumeration value='error'/>
<xs:enumeration value='groupchat'/>
<xs:enumeration value='headline'/>
<xs:enumeration value='normal'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='body'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='subject'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='thread' type='xs:NMTOKEN'/>
<xs:element name='presence'>
<xs:complexType>
<xs:sequence>
<xs:element ref='show'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='status'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='priority'
minOccurs='0'
maxOccurs='1'/>
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<xs:any namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='from'
type='xs:string'
use='optional'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute name='to'
type='xs:string'
use='optional'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='subscribe'/>
<xs:enumeration value='subscribed'/>
<xs:enumeration value='unsubscribe'/>
<xs:enumeration value='unsubscribed'/>
<xs:enumeration value='unavailable'/>
<xs:enumeration value='probe'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='show'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='away'/>
<xs:enumeration value='chat'/>
<xs:enumeration value='dnd'/>
<xs:enumeration value='xa'/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name='status'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
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<xs:attribute ref='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='priority' type='xs:byte'/>
<xs:element name='iq'>
<xs:complexType>
<xs:sequence>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='error'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='from'
type='xs:string'
use='optional'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='required'/>
<xs:attribute name='to'
type='xs:string'
use='optional'/>
<xs:attribute name='type' use='required'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='get'/>
<xs:enumeration value='set'/>
<xs:enumeration value='result'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='error'>
<xs:complexType>
<xs:sequence>
<xs:any namespace='urn:ietf:params:xml:ns:xmpp-stanzas'
maxOccurs='1'/>
<text namespace='urn:ietf:params:xml:ns:xmpp-stanzas'
minOccurs='0'
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maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='code' type='xs:byte' use='optional'/>
<xs:attribute name='type' use='required'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='cancel'/>
<xs:enumeration value='continue'/>
<xs:enumeration value='modify'/>
<xs:enumeration value='auth'/>
<xs:enumeration value='wait'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
</xs:schema>
B.2 jabber:server
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
xmlns:xml='http://www.w3.org/XML/1998/namespace'
targetNamespace='jabber:server'
xmlns='jabber:server'
elementFormDefault='qualified'>
<xs:import namespace='http://www.w3.org/XML/1998/namespace'
schemaLocation='http://www.w3.org/2001/xml.xsd'/>
<xs:element name='message'>
<xs:complexType>
<xs:sequence>
<xs:element ref='subject'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='body'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='thread'
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minOccurs='0'
maxOccurs='1'/>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='from'
type='xs:string'
use='required'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute name='to'
type='xs:string'
use='required'/>
<xs:attribute name='type' use='optional' default='normal'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='chat'/>
<xs:enumeration value='error'/>
<xs:enumeration value='groupchat'/>
<xs:enumeration value='headline'/>
<xs:enumeration value='normal'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='body'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='subject'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute ref='xml:lang' use='optional'/>
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</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='thread' type='xs:NMTOKEN'/>
<xs:element name='presence'>
<xs:complexType>
<xs:sequence>
<xs:element ref='show'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='status'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='priority'
minOccurs='0'
maxOccurs='1'/>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='from'
type='xs:string'
use='required'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute name='to'
type='xs:string'
use='required'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='subscribe'/>
<xs:enumeration value='subscribed'/>
<xs:enumeration value='unsubscribe'/>
<xs:enumeration value='unsubscribed'/>
<xs:enumeration value='unavailable'/>
<xs:enumeration value='probe'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
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<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='show'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='away'/>
<xs:enumeration value='chat'/>
<xs:enumeration value='dnd'/>
<xs:enumeration value='xa'/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name='status'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='priority' type='xs:byte'/>
<xs:element name='iq'>
<xs:complexType>
<xs:sequence>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='error'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='from'
type='xs:string'
use='required'/>
<xs:attribute name='id'
type='xs:NMTOKEN'
use='required'/>
<xs:attribute name='to'
type='xs:string'
use='required'/>
<xs:attribute name='type' use='required'>
<xs:simpleType>
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<xs:restriction base='xs:NCName'>
<xs:enumeration value='get'/>
<xs:enumeration value='set'/>
<xs:enumeration value='result'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='error'>
<xs:complexType>
<xs:sequence>
<xs:any namespace='urn:ietf:params:xml:ns:xmpp-stanzas'
maxOccurs='1'/>
<text namespace='urn:ietf:params:xml:ns:xmpp-stanzas'
minOccurs='0'
maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='code' type='xs:byte' use='optional'/>
<xs:attribute name='type' use='required'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='cancel'/>
<xs:enumeration value='continue'/>
<xs:enumeration value='modify'/>
<xs:enumeration value='auth'/>
<xs:enumeration value='wait'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
</xs:schema>
B.3 session
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
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xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-session'
xmlns='urn:ietf:params:xml:ns:xmpp-session'
elementFormDefault='qualified'>
<xs:element name='session' type='empty'/>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
B.4 jabber:iq:privacy
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:iq:privacy'
xmlns='jabber:iq:privacy'
elementFormDefault='qualified'>
<xs:element name='query'>
<xs:complexType>
<xs:sequence>
<xs:element ref='active'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='default'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='list'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='active'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'>
<xs:attribute name='name'
type='xs:string'
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use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='default'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'>
<xs:attribute name='name'
type='xs:string'
use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='list'>
<xs:complexType>
<xs:sequence>
<xs:element ref='item'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:sequence>
<xs:attribute name='name'
type='xs:string'
use='required'/>
</xs:complexType>
</xs:element>
<xs:element name='item'>
<xs:complexType>
<xs:sequence>
<xs:element ref='iq'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='message'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='presence-in'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='presence-out'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='action' use='required'>
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<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='allow'/>
<xs:enumeration value='deny'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name='order'
type='xs:unsignedInt'
use='required'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='group'/>
<xs:enumeration value='jid'/>
<xs:enumeration value='subscription'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name='value'
type='xs:string'
use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='iq' type='empty'/>
<xs:element name='message' type='empty'/>
<xs:element name='presence-in' type='empty'/>
<xs:element name='presence-out' type='empty'/>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
B.5 jabber:iq:roster
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:iq:roster'
xmlns='jabber:iq:roster'
elementFormDefault='qualified'>
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<xs:element name='query'>
<xs:complexType>
<xs:sequence>
<xs:element ref='item'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='item'>
<xs:complexType>
<xs:sequence>
<xs:element ref='group'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:sequence>
<xs:attribute name='ask' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='subscribe'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name='jid' type='xs:string' use='required'/>
<xs:attribute name='name' type='xs:string' use='optional'/>
<xs:attribute name='subscription' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='to'/>
<xs:enumeration value='from'/>
<xs:enumeration value='both'/>
<xs:enumeration value='none'/>
<xs:enumeration value='remove'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='group' type='xs:string'/>
</xs:schema>
Appendix C. Differences Between Jabber IM/Presence and XMPP
This section is non-normative.
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XMPP has been adapted from the protocols originally developed in the
Jabber open-source community, which can be thought of as "XMPP 0.9".
Because there exists a large installed base of Jabber implementations
and deployments, it may be helpful to specify the key differences
between Jabber and XMPP in order to expedite and encourage upgrades
of those implementations and deployments to XMPP. This section
summarizes the differences that relate specifically to instant
messaging and presence applications, while the corresponding section
of [XMPP-CORE] summarizes the differences that relate to all XMPP
applications.
C.1 Session Establishment
The client-to-server authentication protocol developed in the Jabber
community assumes that every client is an IM client and therefore
initiates an IM session upon successful authentication and resource
binding, which are performed simultaneously (documention of this
protocol is contained in "JEP-0078: Non-SASL Authentication",
published by the Jabber Software Foundation [JSF]). XMPP maintains a
stricter separation between core functionality and IM functionality;
therefore, an IM session is not created until the client specifically
requests one using the protocol defined under Session Establishment
(Section 3).
C.2 Privacy Rules
The Jabber community began to define a protocol for communications
blocking (privacy rules) in late 2001, but that effort was deprecated
once the XMPP Working Group was formed. Therefore the protocol
defined under Blocking Communication (Section 10) is the only such
protocol defined for use in the Jabber community.
Appendix D. Revision History
Note to RFC Editor: please remove this entire appendix, and the
corresponding entries in the table of contents, prior to publication.
D.1 Changes from draft-ietf-xmpp-im-19
o Completed changes necessary to address IESG feedback.
D.2 Changes from draft-ietf-xmpp-im-18
o Added presence type of "probe" to XML schema.
o Added error 'code' attribute to XML schema.
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o Added protocol label registrations for "_im" and "_pres" service
labels.
o Adjusted formatting to conform to RFC Editor requirements.
o Clarified meaning of "connected", "active", and "available"
resources.
D.3 Changes from draft-ietf-xmpp-im-17
o Added missing server handling rules for <user@domain/resource>
cases.
o Further clarified privacy rules syntax by describing child
elements of <item/>.
o Clarified several points related to session establishment.
o Checked all references.
o Completed a thorough proofreading and consistency check of the
entire text.
D.4 Changes from draft-ietf-xmpp-im-16
o Added sentence to make explicit that blocking all communication
includes subscription-related presence stanzas.
o Added clause to make explicit that privacy rules must be applied
before handling of subscription-related presence stanzas and
corresponding generation of roster pushes.
o Added syntax and semantics section for the 'jabber:iq:roster'
namespace.
o Removed content about 'jabber:iq:last' namespace.
o Added several internal references from the security considerations
section to other sections of this document.
o Moved most delivery handling rules from XMPP IM to Extensible
Messaging and Presence Protocol (XMPP): Core.
o Moved detailed stanza syntax descriptions from Extensible
Messaging and Presence Protocol (XMPP): Core to XMPP IM.
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o Moved stanza schemas from Extensible Messaging and Presence
Protocol (XMPP): Core to XMPP IM.
D.5 Changes from draft-ietf-xmpp-im-15
o Specified stream error to be sent to active resource if there is a
conflict regarding session creation.
o Fixed several more typographical errors in the privacy rules
examples.
o Corrected an error regarding server handling of IQ stanzas sent to
bare JIDs.
o Added section on compliance requirements for instant messaging
server and client implementations.
o Added non-normative section on differences between Jabber usage
and XMPP specifications.
D.6 Changes from draft-ietf-xmpp-im-14
o Added subscription state charts.
o Fixed several typographical errors in the privacy rules examples.
o Changed datatype of 'order' attribute in privacy rules from
nonNegativeInteger to unsignedInt.
D.7 Changes from draft-ietf-xmpp-im-13
o Made one small change to privacy list syntax rules.
D.8 Changes from draft-ietf-xmpp-im-12
o Clarified meaning of the default message type as well as handling
of unknown or unsupported types.
o Made several small editorial changes.
D.9 Changes from draft-ietf-xmpp-im-11
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o Further clarified subscription syntax and semantics.
o Further clarified presence responsibilities for clients and
servers.
o Added 'xml:lang' example to presence status.
o Added subsection on presence priority.
o Defined server handling of unsolicited presence stanzas of type
"subscribed".
o Specified default resource priority if not provided.
o Corrected several errors in the schemas.
o Added privacy list business rule regarding roster changes.
o Removed the 'jabber:iq:privacy:error' namespace (not necessary).
o Documented message type='normal'.
o Made numerous small editorial changes throughout.
D.10 Changes from draft-ietf-xmpp-im-10
o Clarified presence responsibilities for servers and clients.
o Clarified the routing and delivery rules for servers.
o Made the 'xml:lang' examples more complete.
o Corrected several errors in the unsubscribe workflow.
o Made small editorial changes in several sections.
D.11 Changes from draft-ietf-xmpp-im-09
o Clarified rules regarding allowable JID types in rosters.
o Further clarified the semantics and routing implications of
presence priorities.
o Removed several obsolete subsections.
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D.12 Changes from draft-ietf-xmpp-im-08
o Removed authorization content (now addressed in Extensible
Messaging and Presence Protocol (XMPP): Core).
o Added protocol for initiating an IM session, including schema and
IANA registration template.
o Corrected <*-condition/> elements to be <condition/>.
o Made small editorial changes to address RFC Editor requirements.
D.13 Changes from draft-ietf-xmpp-im-07
o Added several error cases for resource authorization and updated
relevant schema.
D.14 Changes from draft-ietf-xmpp-im-06
o Specified that IQ result stanzas are required in response to
roster pushes.
o Changed stanza error namespace names to conform to the format
defined in "The IETF XML Registry" as specified in Extensible
Messaging and Presence Protocol (XMPP): Core.
o Removed note to RFC Editor regarding provisional namespace names.
D.15 Changes from draft-ietf-xmpp-im-05
o Removed use of ask='unsubscribe' per list discussion.
o Clarified handling of resource conflict during authorization.
o Added schemas for jabber:iq:auth, jabber:iq:auth:error, and
jabber:iq:privacy:error.
o Corrected several small protocol errors in the examples.
o Clarified semantics of message types.
D.16 Changes from draft-ietf-xmpp-im-04
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o Specified sending of unavailable presence after unsubscribe and
subscription-cancellation actions.
o Further specified syntax and business rules for privacy lists.
o Brought error codes into line with definitions in
draft-ietf-xmpp-core.
o Added note to RFC Editor regarding provisional namespace names.
o Removed vCard content and DTD, instead pointing to JSF
documentation.
D.17 Changes from draft-ietf-xmpp-im-03
o Fixed order processing on privacy rules per list discussion.
o Made numerous small editorial changes.
D.18 Changes from draft-ietf-xmpp-im-02
o Added a great deal more detail to the narrative regarding
server-side privacy rules as well as the interaction between
rosters and subscriptions.
o Removed DTDs in favor of schemas (with the exception of vCard
XML).
o Removed non-normative documentation of authentication using
jabber:iq:auth and of in-band registration using
jabber:iq:register, since these are maintained by the Jabber
Software Foundation and are not part of the XMPP specification.
D.19 Changes from draft-ietf-xmpp-im-01
o Made numerous small editorial changes.
D.20 Changes from draft-ietf-xmpp-im-00
o Moved registration and authentication via jabber:iq:auth to
non-normative appendices.
o Changed initial presence stanza from MUST be empty to SHOULD be
empty.
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o Specified that user or clients should not send presence stanzas of
type='probe'.
o Specified the algorithm for digest passwords.
D.21 Changes from draft-miller-xmpp-im-02
o Added information about the 'jabber:iq:last' protocol to meet the
requirement defined in section 3.2.4 of RFC 2779.
o Added information about the 'jabber:iq:privacy' protocol to meet
the requirement defined in section 2.3.5 of RFC 2779.
o Added information about the vCard XML protocol to meet the
requirement defined in sections 3.1.3 and 4.1.4 of RFC 2779.
o Changed the material describing authentication (but not resource
authorization) with 'jabber:iq:auth' to non-normative.
o Noted that the only watchers are subscribers.
o Nomenclature changes: (1) from "chunks" to "stanzas"; (2) from
"host" to "server"; (3) from "node" to "client" or "user" (as
appropriate).
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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