Network Working Group P. Saint-Andre
Internet-Draft J. Miller
Expires: August 27, 2003 Jabber Software Foundation
February 26, 2003
XMPP Core
draft-ietf-xmpp-core-04
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes the core features of the Extensible Messaging
and Presence Protocol (XMPP), a protocol for streaming XML in near-
real-time that is used mainly for the purpose of instant messaging
(IM) and presence by the servers, clients, and other applications
that comprise the Jabber network.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Discussion Venue . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Intellectual Property Notice . . . . . . . . . . . . . . . . 4
2. Generalized Architecture . . . . . . . . . . . . . . . . . . 5
2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Server . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Client . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4 Gateway . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.5 Network . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Addressing Scheme . . . . . . . . . . . . . . . . . . . . . 7
3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Domain Identifier . . . . . . . . . . . . . . . . . . . . . 7
3.3 Node Identifier . . . . . . . . . . . . . . . . . . . . . . 7
3.4 Resource Identifier . . . . . . . . . . . . . . . . . . . . 8
4. XML Streams . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2 Restrictions . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3 Stream Attributes . . . . . . . . . . . . . . . . . . . . . 10
4.4 Namespace Declarations . . . . . . . . . . . . . . . . . . . 11
4.5 Stream Features . . . . . . . . . . . . . . . . . . . . . . 12
4.6 Stream Errors . . . . . . . . . . . . . . . . . . . . . . . 12
4.7 Simple Streams Example . . . . . . . . . . . . . . . . . . . 14
5. Stream Encryption . . . . . . . . . . . . . . . . . . . . . 16
5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.2 Narrative . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.3 Client-Server Protocol . . . . . . . . . . . . . . . . . . . 17
5.4 Certificate-Based Authentication . . . . . . . . . . . . . . 19
6. Stream Authentication . . . . . . . . . . . . . . . . . . . 20
6.1 SASL Authentication . . . . . . . . . . . . . . . . . . . . 20
6.1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.1.2 Narrative . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.1.3 SASL Definition . . . . . . . . . . . . . . . . . . . . . . 22
6.1.4 Client-Server Protocol . . . . . . . . . . . . . . . . . . . 23
6.2 Dialback Authentication . . . . . . . . . . . . . . . . . . 25
6.2.1 Dialback Protocol . . . . . . . . . . . . . . . . . . . . . 27
7. XML Stanzas . . . . . . . . . . . . . . . . . . . . . . . . 31
7.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.2 Common Attributes . . . . . . . . . . . . . . . . . . . . . 31
7.2.1 to . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.2.2 from . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.2.3 id . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.2.4 type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
7.2.5 xml:lang . . . . . . . . . . . . . . . . . . . . . . . . . . 32
7.3 Message Stanzas . . . . . . . . . . . . . . . . . . . . . . 32
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7.3.1 Types of Message . . . . . . . . . . . . . . . . . . . . . . 32
7.3.2 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 33
7.4 Presence Stanzas . . . . . . . . . . . . . . . . . . . . . . 34
7.4.1 Types of Presence . . . . . . . . . . . . . . . . . . . . . 34
7.4.2 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 35
7.5 IQ Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.5.2 Types of IQ . . . . . . . . . . . . . . . . . . . . . . . . 37
7.5.3 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.6 Extended Namespaces . . . . . . . . . . . . . . . . . . . . 38
8. XML Usage within XMPP . . . . . . . . . . . . . . . . . . . 40
8.1 Namespaces . . . . . . . . . . . . . . . . . . . . . . . . . 40
8.2 Validation . . . . . . . . . . . . . . . . . . . . . . . . . 40
8.3 Character Encodings . . . . . . . . . . . . . . . . . . . . 40
8.4 Inclusion of Text Declaration . . . . . . . . . . . . . . . 40
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 41
10. Internationalization Considerations . . . . . . . . . . . . 42
11. Security Considerations . . . . . . . . . . . . . . . . . . 43
11.1 Client-to-Server Communications . . . . . . . . . . . . . . 43
11.2 Server-to-Server Communications . . . . . . . . . . . . . . 43
11.3 Firewalls . . . . . . . . . . . . . . . . . . . . . . . . . 43
11.4 Minimum Security Mechanisms . . . . . . . . . . . . . . . . 43
References . . . . . . . . . . . . . . . . . . . . . . . . . 45
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 47
A. Standard Error Codes . . . . . . . . . . . . . . . . . . . . 48
B. XML Schemas . . . . . . . . . . . . . . . . . . . . . . . . 51
B.1 streams namespace . . . . . . . . . . . . . . . . . . . . . 51
B.2 SASL namespace . . . . . . . . . . . . . . . . . . . . . . . 52
B.3 Dialback namespace . . . . . . . . . . . . . . . . . . . . . 52
B.4 jabber:client namespace . . . . . . . . . . . . . . . . . . 54
B.5 jabber:server namespace . . . . . . . . . . . . . . . . . . 56
C. Revision History . . . . . . . . . . . . . . . . . . . . . . 60
C.1 Changes from draft-ietf-xmpp-core-03 . . . . . . . . . . . . 60
C.2 Changes from draft-ietf-xmpp-core-02 . . . . . . . . . . . . 60
C.3 Changes from draft-ietf-xmpp-core-01 . . . . . . . . . . . . 60
C.4 Changes from draft-ietf-xmpp-core-00 . . . . . . . . . . . . 60
C.5 Changes from draft-miller-xmpp-core-02 . . . . . . . . . . . 61
Full Copyright Statement . . . . . . . . . . . . . . . . . . 63
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1. Introduction
1.1 Overview
The Extensible Messaging and Presence Protocol (XMPP) is an open XML
[1] protocol for near-real-time messaging, presence, and request-
response services. The protocol was developed originally within the
Jabber community starting in 1998, and since 2001 has continued to
evolve under the auspices of the Jabber Software Foundation [2] and
now the XMPP WG. The current document defines the core features of
XMPP; XMPP IM [3] defines the extensions necessary to provide the
instant messaging (IM) and presence functionality defined in RFC 2779
[4].
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 [5].
1.3 Discussion Venue
The authors welcome discussion and comments related to the topics
presented in this document. The preferred forum is the
<xmppwg@jabber.org> mailing list, for which archives and subscription
information are available at <http://www.jabber.org/cgi-bin/mailman/
listinfo/xmppwg/>.
1.4 Intellectual Property Notice
This document is in full compliance with all provisions of Section 10
of RFC 2026. Parts of this specification use the term "jabber" for
identifying namespaces and other protocol syntax. Jabber[tm] is a
registered trademark of Jabber, Inc. Jabber, Inc. grants permission
to the IETF for use of the Jabber trademark in association with this
specification and its successors, if any.
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2. Generalized Architecture
2.1 Overview
Although XMPP is not wedded to any specific network architecture, to
this point it has usually been implemented via a typical client-
server architecture, wherein a client utilizing XMPP accesses a
server over a TCP [6] 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 to manage
connections from or sessions for other entities (in the form of XML
streams to and from authorized clients, servers, and other entities)
and to route appropriately-addressed XML data "stanzas" 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 users of XMPP-based IM 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. Compliant server
implementations MUST ensure in-order processing of XML stanzas
received from connected clients, servers, and services.
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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 it must be noted that there is
no necessary coupling of an XML stream to a TCP socket (e.g., a
client COULD connect via HTTP polling or some other mechanism).
Multiple resources (e.g., devices or locations) MAY connect
simultaneously to a server on behalf of each authorized client, with
each resource connecting over a discrete TCP socket and
differentiated by the resource identifier of a JID (Section 3) (e.g.,
user@domain/home vs. user@domain/work). The port assigned by the
IANA [7] for connections between a Jabber client and a Jabber server
is 5222. For further details about client-to-server communications
expressly for the purpose of instant messaging and presence, refer to
XMPP IM [3].
2.4 Gateway
A gateway is a special-purpose server-side service whose primary
function is to translate XMPP into the protocol(s) of another
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), SMTP, and foreign instant messaging networks
such as Yahoo!, MSN, ICQ, and AIM. 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 (typically a
DNS hostname) 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. The usual method for providing a
connection between two servers is to open a TCP socket on the IANA-
assigned port 5269 and to negotiate a connection using the Dialback
Protocol (Section 6.2) defined in this document.
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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 [8]. In particular, a valid Jabber
Identifier (JID) contains a set of ordered elements formed of a
domain identifier, node identifier, and resource identifier in the
following format: [node@]domain[/resource].
All JIDs are based on the foregoing structure. The most common use
of this structure is to identify an IM user, the server to which the
user connects, and the user's active session or connection (e.g., a
specific client) in the form of user@domain/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).
3.2 Domain Identifier
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 (a multi-user chat service, a
user directory, a gateway to a foreign messaging system, etc.).
The domain identifier for every server or service that will
communicate over a network SHOULD resolve to a Fully Qualified Domain
Name. A domain identifier MUST conform to RFC 952 [9] and RFC 1123
[10]. A domain identifier MUST be no more than 1023 bytes in length,
and is subject to comparison in accordance with the rules defined in
the nameprep [11] profile of stringprep [12].
3.3 Node Identifier
The node identifier is an optional secondary identifier. 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 multi-user chat room
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associated with a multi-user chat service). The entity represented
by a node identifier is addressed within the context of a specific
domain; in the context of IM users this address is called a "bare
JID" and is of the form <user@domain>.
A node identifier MUST be no more than 1023 bytes in length and MUST
conform to the nodeprep [13] profile of stringprep [12].
3.4 Resource Identifier
The resource identifer is an optional third identifier. It
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. An entity
may maintain multiple resources simultaneously.
A resource identifier MUST be no more than 1023 bytes in length and
MUST conform to the resourceprep [14] profile of stringprep [12].
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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, as a result,
discrete units of structured information that are referred to as "XML
stanzas". (Note: in this overview we use the example of
communications between a client and server; however XML streams are
more generalized and may be used for communications from server to
server and from service to server as well.)
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 supported and the
character encoding. A compliant entity SHOULD accept any namespace
prefix on the <stream/> element; however, for historical reasons some
entities MAY accept only a 'stream' prefix, resulting in use of a
<stream:stream/> element. The server SHOULD then reply with a second
XML stream back to the client, again optionally preceded by a text
declaration.
Within the context of an XML stream, a sender is able to send a
discrete semantic unit of structured information to any recipient.
This unit of structured information is a well-balanced XML stanza,
such as a message, presence, or IQ stanza (a stanza of an XML
document is said to be well-balanced if it matches production [43]
content of the XML specification [1]). These stanzas exist at the
direct child level of the root <stream/> element. The start of any
XML stanza is unambiguously denoted by the element start tag at
depth=1 (e.g., <presence>), and the end of any XML stanza is
unambiguously denoted by the corresponding close tag at depth=1
(e.g., </presence>). Each XML stanza MAY contain child elements or
CDATA sections as necessary in order to convey the desired
information from the sender to the recipient. The session is closed
at the client's request by sending a closing </stream> tag to the
server (a session may also be closed by the server).
Thus a client's session with a server can be seen as two open-ended
XML documents that are built up through the accumulation of the XML
stanzas sent over the course of the session (one from the client to
the server and one from the server to the client), and the root
<stream/> element can be considered the document entity for those
streams. In essence, then, an XML stream acts as an envelope for all
the XML stanzas sent during a session. We can represent this
graphically as follows:
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|-------------------|
| <stream> |
|-------------------|
| <message to=''> |
| <body/> |
| </message> |
|-------------------|
| <presence to=''> |
| <show/> |
| </presence> |
|-------------------|
| <iq to=''> |
| <query/> |
| </iq> |
|-------------------|
| ... |
|-------------------|
| </stream> |
|-------------------|
4.2 Restrictions
XML streams are used to transport a subset of XML. Specifically, XML
streams SHOULD NOT contain processing instructions, predefined
entities (as defined in Section 4.6 of the XML specification [1]),
comments, or DTDs. Any such XML data SHOULD be ignored by a
compliant implementation.
4.3 Stream Attributes
The attributes of the stream element are as follows (we now
generalize the endpoints by using the terms "initiating entity" and
"receiving entity"):
o to -- The 'to' attribute SHOULD be used only in the XML stream
from the initiating entity to the receiving entity, and MUST be
set to the JID of the receiving entity. There SHOULD be no 'to'
attribute set in the XML stream by which the receiving entity
replies to the initiating entity; however, if a 'to' attribute is
included, it SHOULD be ignored by the initiating entity.
o from -- The 'from' attribute SHOULD be used only in the XML stream
from the receiving entity to the initiating entity, and MUST be
set to the JID of the receiving entity granting access to the
initiating entity. There SHOULD be no 'from' attribute on the XML
stream sent from the initiating entity to the receiving entity;
however, if a 'from' attribute is included, it SHOULD be ignored
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by the receiving entity.
o id -- The 'id' attribute SHOULD be used only in the XML stream
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 session
with the receiving entity. There SHOULD be no 'id' attribute on
the XML stream sent from the initiating entity to the receiving
entity; however, if an 'id' attribute is included, it SHOULD be
ignored by the receiving entity.
o version -- The 'version' attribute MAY be used in the XML stream
from the initiating entity to the receiving entity in order signal
compliance with the protocol defined herein; this is done by
setting the value of the attribute to "1.0". If the initiating
entity includes the version attribute, the receiving entity MUST
reciprocate by including the attribute in its response (if the
receiving entity supports XMPP 1.0).
We can summarize these values as follows:
| initiating to receiving | receiving to initiating
------------------------------------------------------------
to | JID of receiver | ignored
from | ignored | JID of receiver
id | ignored | session key
version | signals XMPP 1.0 support | signals XMPP 1.0 support
4.4 Namespace Declarations
The stream element MAY also contain namespace declarations as defined
in the XML namespaces specification [15].
A default namespace declaration ('xmlns') is REQUIRED and is used in
both XML streams in order to scope the allowable first-level children
of the root stream element for both streams. This namespace
declaration MUST be the same for the initiating stream and the
responding stream so that both streams are scoped consistently. The
default namespace declaration applies to the stream and all stanzas
sent within a stream.
A stream namespace declaration (e.g., 'xmlns:stream') is REQUIRED in
both XML streams. A compliant entity SHOULD accept any namespace
prefix on the <stream/> element; however, for historical reasons some
entities MAY accept only a 'stream' prefix, resulting in use of a
<stream:stream/> element as the stream root. The name of the stream
namespace MUST be "http://etherx.jabber.org/streams".
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XML streams function as containers for any XML stanzas sent
asynchronously between network endpoints. It should be possible to
scope an XML stream with any default namespace declaration, i.e., it
should be possible to send any properly-namespaced XML stanza over an
XML stream. A compliant implementation MUST support the following
two namespaces (for historical reasons, existing 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
o jabber:server -- this default namespace is declared when the
stream is used for communications between two servers
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 scoped by the 'jabber:client' or 'jabber:server' namespace, it
MUST support all three core stanza types (message, presence, and IQ)
as described herein and defined in the schema.
4.5 Stream Features
The root stream element MAY contain a features child element (e.g.,
<stream:features/> if the stream namespace prefix is 'stream'). This
is used to communicate generic stream-level capabilities including
stream-level features that can be negotiated as the streams are set
up. If the initiating entity sends a "version='1.0'" attribute in
its initiating stream element, the receiving entity MUST send a
features child element to the initiating entity if there are any
capabilities that need to be advertised or features that can be
negotiated for the stream. Currently this is used for SASL and TLS
negotiation only, but it could be used for other negotiable features
in the future (usage is defined under Stream Encryption (Section 5)
and Stream Authentication (Section 6) below). If an entity does not
understand or support some features, it SHOULD ignore them.
4.6 Stream Errors
The root stream element MAY contain an error child element (e.g.,
<stream:error/> if the stream namespace prefix is 'stream'). The
error child MUST be sent by a Jabber entity (usually a server rather
than a client) if it perceives that a stream-level error has
occurred. Examples of error conditions include the sending of
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invalid XML, the shutdown of a server, an internal server error such
as the shutdown of a session manager, and inclusion of an unsupported
version number in the initiating stream header. 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 and then send a closing
</stream> tag. Specifically, XML of the following form is sent
within the context of an existing stream (the error element MUST
possess the 'code' attribute):
<stream:stream ...>
...
<stream:error code='400'/>
</stream:stream>
If the error occurs while the stream is being set up, the receiving
entity MUST still send the opening and closing stream tags and
include the error element as a child of the stream element. The
following example illustrates this principle (where the "C" lines are
sent from the client to the server, and the "S" lines are sent from
the server to the client):
C: <stream:stream
to='somedomain'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='bad.version'>
S: <stream:stream
from='somedomain'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
S: <stream:error code='505'/>
S: </stream:stream>
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.
The following codes are defined for stream-level errors:
o 302 - Redirect
o 400 - Bad XML
o 404 - Unknown Host
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o 410 - Gone
o 500 - Internal Server Error
o 505 - Version Not Supported
If the error is 302 ("Redirect"), the server SHOULD include CDATA
specifying the alternate hostname or IP address to which the
initiating entity may attempt to connect.
4.7 Simple Streams Example
The following is 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):
A basic session:
C: <?xml version='1.0'?>
<stream:stream
to='server'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
S: <?xml version='1.0'?>
<stream:stream
from='server'
id='id_123456789'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
... authentication ...
C: <message from='alex@graham-bell' to='watson@graham-bell'>
C: <body>Watson come here, I want you!</body>
C: </message>
S: <message from='watson@graham-bell' to='alex@graham-bell'>
S: <body>I'm on my way!</body>
S: </message>
C: </stream:stream>
S: </stream:stream>
These are in actuality a sending stream and a receiving stream, which
can be viewed a-chronologically as two XML documents:
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C: <?xml version='1.0'?>
<stream:stream
to='server'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
C: <message from='alex@graham-bell' to='watson@graham-bell'>
C: <body>Watson come here, I want you!</body>
C: </message>
C: </stream:stream>
S: <?xml version='1.0'?>
<stream:stream
from='server'
id='id_123456789'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
S: <message from='watson@graham-bell' to='alex@graham-bell'>
S: <body>I'm on my way!</body>
S: </message>
S: </stream:stream>
A session gone bad:
C: <?xml version='1.0'?>
<stream:stream
to='server'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
S: <?xml version='1.0'?>
<stream:stream
from='server'
id='id_123456789'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
C: <message><body>Bad XML, no closing body tag!</message>
S: <stream:error code='400'/>
S: </stream:stream>
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5. Stream Encryption
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) [17] protocol, along with a "STARTTLS"
extension that is modelled on similar extensions for the IMAP [18],
POP3 [19], and ACAP [20] protocols as described in RFC 2595 [21].
The namespace identifier for the STARTTLS extension is 'http://
www.ietf.org/rfc/rfc2595.txt'. TLS may be used between any
initiating entity and any receiving entity (e.g., a stream from a
client to a server or from one server to another).
The following rules MUST be observed:
1. If the initiating entity is capable of using the STARTTLS
extension, it MUST include the "version='1.0'" flag in the
initiating stream header.
2. If the receiving entity is capable of using the STARTTLS
extension, it MUST send the <starttls/> element in the defined
namespace along with the list of features that it sends in
response to the opening stream tag received from the initiating
entity.
3. If the initiating entity chooses to use TLS for stream
encryption, TLS negotiation MUST be completed before proceeding
to authenticate the stream using SASL.
4. If TLS is used for stream encryption, the receiving entity MUST
close the stream whether the TLS negotiation results in success
or failure.
5. If the TLS negotiation is successful, TLS takes effect
immediately following the closing ">" character of the <starttls/
> element for the client and immediately following the closing
">" character of the <proceed> element for the server. A new
stream MUST then be initiated by the initiating entity.
6. If the TLS negotiation is successful, the receiving entity MUST
discard any knowledge obtained from the initiating entity before
TLS takes effect.
7. If the TLS negotiation is successful, the initiating entity MUST
discard any knowledge obtained from the receiving entity before
TLS takes effect.
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8. 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.
9. If TLS is used for stream encryption, SASL MUST NOT be used for
anything but stream authentication (i.e., a security layer MUST
NOT be negotiated using SASL). Conversely, if a security layer
is to be negotiated via SASL, TLS MUST NOT be used.
5.2 Narrative
When a client secures a stream with a server, the steps involved are
as follows:
1. The client opens a TCP connection and initiates the stream by
sending the opening XML stream header to the server, including
the "version='1.0'" flag.
2. The server responds by opening a TCP connection and sending an
XML stream header to the client.
3. The server offers the STARTTLS extension to the client by sending
it along with the list of supported stream features.
4. The client issues the STARTTLS command to instruct the server
that it wishes to begin a TLS negotiation to secure the stream.
5. The server MUST reply with either an empty <proceed/> element or
an empty <failure/> element, but keep the underlying TCP
connection open.
6. The client begins a TLS negotiation in accordance with RFC 2246
[17]. Upon completion of the negotiation, the client initiates a
new stream by sending a new opening XML stream header to the
server.
7. The server responds by sending an XML stream header to the client
along with the remaining available features (but NOT including
the STARTTLS element).
5.3 Client-Server Protocol
The following example shows the data flow for a client securing a
stream using STARTTLS.
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Step 1: Client initiates stream to server:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='capulet.com'
version='1.0'>
Step 2: Server responds by sending a stream tag to the client:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='12345678'
version='1.0'>
Step 3: Server sends the STARTTLS extension to the client along with
authentication mechanisms and any other stream features:
<stream:features>
<starttls xmlns='http://www.ietf.org/rfc/rfc2595.txt'/>
<mechanisms xmlns='http://www.iana.org/assignments/sasl-mechanisms'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
</mechanisms>
</stream:features>
Step 4: Client sends the STARTTLS command to the server:
<starttls xmlns='http://www.ietf.org/rfc/rfc2595.txt'/>
Step 5: Server informs client to proceed:
<proceed xmlns='http://www.ietf.org/rfc/rfc2595.txt'/>
Step 5 (alt): Server informs client that TLS negotiation has faile
has failedd:
<failure xmlns='http://www.ietf.org/rfc/rfc2595.txt'/>
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Step 6: Client and server complete TLS negotiation via TCP. When
finished, the client initiates a new stream to the server:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='capulet.com'
version='1.0'>
Step 7: Server responds by sending a stream header to the client
along with any remaining negotiatiable stream features:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='12345678'
version='1.0'>
<stream:features>
<mechanisms xmlns='http://www.iana.org/assignments/sasl-mechanisms'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
<mechanism>EXTERNAL</mechanism>
</mechanisms>
</stream:features>
5.4 Certificate-Based Authentication
If the client presents a valid client certificate during the TLS
negotiation, the server MAY offer the SASL EXTERNAL mechanism to the
client during stream authentication. (see RFC 2222 [16]). If the
client selects this mechanism for authentication, the authentication
credentials shall be taken from the presented certificate.
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6. Stream Authentication
XMPP includes two methods for enforcing authentication at the level
of XML streams. When one entity is already known to another (i.e.,
there is an existing trust relationship between the entities such as
that established when a user registers with a server or an
administrator configures a server to trust another server), the
preferred method for authenticating streams between the two entities
uses an XMPP adaptation of the Simple Authentication and Security
Layer (SASL) [16]. When there is no existing trust relationship
between the two entities, such trust MAY be established based on
existing trust in DNS; the authentication method used when two such
entities are servers is the server dialback protocol that is native
to XMPP (no such ad-hoc method is defined between a client and a
server). Both of these methods are described in this section.
Stream authentication is REQUIRED for all direct communications
between two entities; if an entity sends a stanza to an
unauthenticated stream, the receiving entity SHOULD silently drop the
stanza and MUST NOT process it.
6.1 SASL Authentication
6.1.1 Overview
The Simple Authentication and Security Layer (SASL) provides a
generalized method for adding authentication support to connection-
based protocols. XMPP uses a generic XML namespace profile for SASL
that conforms to section 4 ("Profiling Requirements") of RFC 2222
[16] (the namespace identifier for this protocol is 'http://
www.iana.org/assignments/sasl-mechanisms').
The following rules MUST be observed:
1. If TLS is used for stream encryption, SASL MUST NOT be used for
anything but stream authentication (i.e., a security layer MUST
NOT be negotiated using SASL). Conversely, if a security layer
is to be negotiated via SASL, TLS MUST NOT be used.
2. If the initiating entity is capable of authenticating via SASL,
it it MUST include the "version='1.0'" flag in the initiating
stream header.
3. If the receiving entity is capable of accepting authentications
via SASL, it MUST send one or more authentication mechanisms
within a <mechanisms/> element in response to the opening stream
tag received from the initiating entity.
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4. If the SASL negotiation 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.
5. If the SASL negotiation 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.
6.1.2 Narrative
When a client authenticates with a server, the steps involved are as
follows:
1. The client requests SASL authentication by including a 'version'
attribute in the opening XML stream header sent to the server,
with the value set to "1.0".
2. After sending an XML stream header in response, the server sends
a list of available SASL authentication mechanisms, each of which
is a <mechanism/> element included as a child within a
<mechanisms/> container element that is sent as a child of the
first-level <features/> element. If channel encryption must be
established before a particular authentication mechanism may be
used, the server MUST NOT provide that mechanism in the list of
available SASL authentication methods.
3. The client selects a mechanism by sending an <auth/> element to
the server; this element MAY optionally contain character data
(in SASL terminology the "initial response") if the mechanism
supports or requires it.
4. If necessary, the server challenges the client by sending a
<challenge/> element to the client; this element MAY optionally
contain character data.
5. The client responds to the challenge by sending a <response/>
element to the server; this element MAY optionally contain
character data.
6. If necessary, the server sends more challenges and the client
sends more responses.
This series of challenge/response pairs continues until one of three
things happens:
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1. The client aborts the handshake by sending an <abort/> element to
the server.
2. The server reports failure of the handshake by sending a
<failure/> element to the client. The particular cause of
failure optionally may be communicated in the 'code' attribute of
the <failure/> element, and may be any one of 432 (password
transition is needed), 534 (authentication mechanism is too
weak), or 454 (temporary authentication failure).
3. The server reports success of the handshake by sending a
<success/> element to the client; this element MAY optionally
contain character data (in SASL terminology "additional data with
success").
Any character data contained within these elements MUST be encoded
using base64.
6.1.3 SASL Definition
Section 4 of the SASL specification [16] requires 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
'mechanism' attribute possesed 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.
security layer negotiation: If a security layer is negotiated, both
sides consider the original stream closed and new <stream/>
headers are sent by both entities. The security layer takes
effect immediately following the ">" character of the empty
<response/> element for the client and immediately following the
closing ">" character of the <succeed/> element for the server.
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use of the authorization identity: The authorization identity, if
present, is unused by xmpp.
6.1.4 Client-Server Protocol
The following example shows the data flow for a client authenticating
with a server using SASL.
Step 1: Client initiates stream to server:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='domain'
version='1.0'>
Step 2: Server responds with a stream tag sent to the client:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='12345678'
from='domain'
version='1.0'>
Step 3: Server informs client of available authentication mechanisms:
<stream:features>
<mechanisms xmlns='http://www.iana.org/assignments/sasl-mechanisms'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
</mechanisms>
</stream:features>
Step 4: Client selects an authentication mechanism ("initial
response"):
<auth
xmlns='http://www.iana.org/assignments/sasl-mechanisms'
mechanism='DIGEST-MD5'/>
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Step 5: Server sends a base64-encoded challenge to the client:
<challenge xmlns='http://www.iana.org/assignments/sasl-mechanisms'>
cmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik9BNk1HOXRFUUdtMmhoIi
xxb3A9ImF1dGgiLGNoYXJzZXQ9dXRmLTgsYWxnb3JpdGhtPW1kNS1zZXNz
</challenge>
The decoded challenge is:
realm="cataclysm.cx",nonce="OA6MG9tEQGm2hh",\ qop="auth",charset=utf-
8,algorithm=md5-sess
Step 6: Client responds to the challenge:
<response xmlns='http://www.iana.org/assignments/sasl-mechanisms'>
dXNlcm5hbWU9InJvYiIscmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik
9BNk1HOXRFUUdtMmhoIixcIGNub25jZT0iT0E2TUhYaDZWcVRyUmsiLG5j
PTAwMDAwMDAxLHFvcD1hdXRoLFwgZGlnZXN0LXVyaT0ieG1wcC9jYXRhY2
x5c20uY3giLFwgcmVzcG9uc2U9ZDM4OGRhZDkwZDRiYmQ3NjBhMTUyMzIxZ
jIxNDNhZjcsY2hhcnNldD11dGYtOA==
</response>
The decoded response is:
username="rob",realm="cataclysm.cx",nonce="OA6MG9tEQGm2hh",\
cnonce="OA6MHXh6VqTrRk",nc=00000001,qop=auth,\ digest-uri="xmpp/
cataclysm.cx",\
response=d388dad90d4bbd760a152321f2143af7,charset=utf-8
Step 7: Server sends another challenge to the client:
<challenge xmlns='http://www.iana.org/assignments/sasl-mechanisms'>
cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZA==
</challenge>
The decoded challenge is:
rspauth=ea40f60335c427b5527b84dbabcdfffd
Step 8: Client responds to the challenge:
<response xmlns='http://www.iana.org/assignments/sasl-mechanisms'/>
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Step 9: Server informs client of successful authentication:
<success xmlns='http://www.iana.org/assignments/sasl-mechanisms'/>
Step 9 (alt): Server informs client of failed authentication:
<failure code='454'
xmlns='http://www.iana.org/assignments/sasl-mechanisms'/>
Step 10: Client initiates a new stream to the server:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='domain'
version='1.0'>
Step 11: Server responds by sending a stream header to the client,
with the stream already authenticated (not followed by further stream
features):
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='12345678'
from='domain'
version='1.0'>
6.2 Dialback Authentication
XMPP includes a protocol-level method for verifying that a connection
between two servers can be trusted (at least as much as the DNS can
be trusted). The method is called dialback and is used only within
XML streams that are declared under the "jabber:server" namespace.
The purpose of the dialback protocol is to make server spoofing more
difficult, and thus to make it more difficult to forge XML stanzas.
Dialback is not intended as a mechanism for securing or encrypting
the streams between servers, only for helping to prevent the spoofing
of a server and the sending of false data from it. Dialback is made
possible by the existence of DNS, since one server can verify that
another server which is connecting to it is authorized to represent a
given server on the Jabber network. All DNS hostname resolutions
MUST first resolve the hostname using an SRV [23] record of
_jabber._tcp.server. If the SRV lookup fails, the fallback is a
normal A lookup to determine the IP address, using the jabber-server
port of 5269 assigned by the Internet Assigned Numbers Authority [7].
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Note that the method for generating and verifying the keys used in
the dialback protocol MUST take into account the hostnames being
used, along with a secret known only by the receiving server and the
random ID generated for the stream. Generating unique but verifiable
keys is important to prevent common man-in-the-middle attacks and
server spoofing.
In the description that follows we use the following terminology:
o Originating Server -- the server that is attempting to establish a
connection between the two servers
o Receiving Server -- the server that is trying to authenticate that
Originating Server represents the Jabber server which it claims to
be
o Authoritative Server -- the server that is given when a DNS lookup
is performed on the name that Originating Server initially gave;
for basic environments this will be Originating Server, but it
could be a separate machine in Originating Server's network
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.
4. Receiving Server sends the same 'key' value to Authoritative
Server.
5. Authoritative Server replies that key is valid or invalid.
6. Receiving Server tells Originating Server whether it is
authenticated or not.
We can represent this flow of events graphically as follows:
Originating Receiving
Server Server
----------- ---------
| |
| establish connection |
| ----------------------> |
| |
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| send stream header |
| ----------------------> |
| |
| establish connection |
| <---------------------- |
| |
| send stream header |
| <---------------------- |
| | Authoritative
| send dialback key | Server
| ----------------------> | -------------
| | |
| establish connection |
| ----------------------> |
| |
| send stream header |
| ----------------------> |
| |
| establish connection |
| <---------------------- |
| |
| send stream header |
| <---------------------- |
| |
| send dialback key |
| ----------------------> |
| |
| validate dialback key |
| <---------------------- |
|
| report dialback result |
| <---------------------- |
| |
6.2.1 Dialback Protocol
The traffic sent 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
(the 'to' and 'from' attributes are NOT REQUIRED on the root
stream element):
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<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'>
Note: the value of the xmlns:db namespace declaration indicates
to Receiving Server that Originating Server supports dialback.
3. Receiving Server sends a stream header back to Originating
Server (the 'to' and 'from' attributes are NOT REQUIRED on the
root stream element):
<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'
id='457F9224A0...'>
4. Originating Server sends a dialback key to Receiving Server:
<db:result
to='Receiving Server'
from='Originating Server'>
98AF014EDC0...
</db:result>
Note: this key is not examined by Receiving Server, since
Receiving Server does not keep information about Originating
Server between sessions.
5. Receiving Server now establishes a connection back to
Originating Server, getting Authoritative Server.
6. Receiving Server sends Authoritative Server a stream header (the
'to' and 'from' attributes are NOT REQUIRED on the root stream
element):
<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'>
7. Authoritative Server sends Receiving Server a stream header:
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<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'
id='1251A342B...'>
8. Receiving Server sends Authoritative Server a stanza indicating
it wants Authoritative Server to 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 2, and the key Originating Server gave Receiving Server in
step 3. Based on this information and shared secret information
within the 'Originating Server' network, the key is verified.
Any verifiable method can be used to generate the key.
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'
type='invalid'
id='457F9224A0...'/>
10. Receiving Server informs Originating Server of the result:
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<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. Once 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 dropped. As a final guard against
domain spoofing, Receiving Server MUST verify that all XML
stanzas received from Originating Server include a 'from'
attribute and that the value of that attribute includes the
validated domain. In addition, all XML stanzas MUST include a
'to' attribute.
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7. XML Stanzas
7.1 Overview
Once the XML streams in each direction have been authenticated and
(if desired) encrypted, XML stanzas can be sent over the streams.
XML stanzas are the three core data elements for XMPP communications:
<message/>, <presence/>, and <iq/>. These elements are sent as
direct (depth=1) children of the root <stream/> element and are
scoped by one of the default namespaces identified in Section 4.4.
7.2 Common Attributes
Five attributes are common to message, presence, and IQ stanzas.
These are defined below.
7.2.1 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) MAY legitimately lack a 'to'
attribute. In the 'jabber:server' namespace, a stanza MUST possess a
'to' attribute.
7.2.2 from
The 'from' attribute specifies the JID of the sender.
In the 'jabber:client' namespace, a client MUST NOT include a 'from'
attribute on the stanzas it sends to a server; if a server receives a
stanza from a client and the stanza possesses a 'from' attribute, it
MUST ignore the value of the 'from' attribute. In addition, a server
MUST stamp stanzas received from a client with the user@domain/
resource (full JID) of the connected resource that generated the
stanza.
In the 'jabber:server' namespace, a stanza MUST possess a 'from'
attribute. In particular, a server MUST include a 'from' attribute
on stanzas it routes to other servers. The domain identifier of the
JID contained in the 'from' attribute MUST match the hostname of the
server as communicated in the dialback negotiation (or a subdomain
thereof).
7.2.3 id
The optional 'id' attribute MAY be used to track stanzas sent and
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received. The 'id' attribute is generated by the sender. An 'id'
attribute included in an IQ request of type "get" or "set" SHOULD be
returned to the sender in any IQ response of type "result" or "error"
generated by the recipient of the request. A recipient of a message
or presence stanza MAY return that 'id' in any replies, but is NOT
REQUIRED to do so.
The value of the 'id' attribute is not intended to be unique --
globally, within a domain, or within a stream. It is generated by a
sender only for internal tracking of information within the sending
application.
7.2.4 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, and thus are specified in
the following sections.
7.2.5 xml:lang
Any message or presence stanza MAY possess an 'xml:lang' attribute
specifying the default language of any CDATA sections of the stanza
or its child elements. An IQ stanza SHOULD NOT possess an 'xml:lang'
attribute, since it is merely a vessel for data in other namespaces
and does not itself contain children that have CDATA. The value of
the 'xml:lang' attribute MUST be an NMTOKEN and MUST conform to the
format defined in RFC 3066 [22].
7.3 Message Stanzas
Message stanzas in the 'jabber:client' or 'jabber:server' namespace
are used to "push" information to another entity. Common uses in the
context of instant messaging 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. These messages
types are identified more fully below.
7.3.1 Types of Message
The 'type' attribute of a message stanza is OPTIONAL; if included, it
specifies the conversational context of the message. The sending of
a message stanza without a 'type' attribute signals that the message
stanza is a single message. However, the 'type' attribute MAY also
have one of the following values:
o chat -- The message is sent in the context of a one-to-one chat
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conversation.
o groupchat -- The message is sent in the context of a multi-user
chat environment.
o headline -- The message is generated by an automated service that
delivers content (news, sports, market information, etc.).
o error - A message returned to a sender specifying an error
associated with a previous message sent by the sender (for a full
list of error messages, see error codes (Appendix A)).
For detailed information about the meaning of these message types,
refer to XMPP IM [3].
7.3.2 Children
As described under extended namespaces (Section 7.6), a message
stanza MAY contain any properly-namespaced child element as long as
the namespace name is not "jabber:client", "jabber:server", or
"http://etherx.jabber.org/streams", and as long as the element name
does not match that of one of the core data elements, stream
elements, or defined children thereof.
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. Specifically, if a message stanza has no 'type' attribute
or has a 'type' attribute with a value of "chat", "groupchat", or
"headline", it MAY contain any of the following child elements
without an explicit namespace declaration:
o body -- The textual contents of the message; 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.
o subject -- The subject 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 value. The
<subject> element MUST NOT contain mixed content.
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o thread -- A random string that is generated by the sender and that
SHOULD be copied back in replies; it is used for tracking a
conversation thread (sometimes referred to as an "IM session")
between two entities. If used, it MUST be unique to that
conversation thread within the stream and MUST be consistent
throughout that conversation. The use of the <thread/> element is
optional and is not used to identify individual messages, only
conversations. The method for generating thread IDs SHOULD be as
follows: (1) concatenate the sender's full JID (user@host/
resource) with the recipient's full JID; (2) concatenate these JID
strings with a full ISO-8601 timestamp including year, month, day,
hours, minutes, seconds, and UTC offset in the following format:
yyyy-mm-dd-Thh:mm:ss-hh:mm; (3) hash the resulting string
according to the SHA1 algorithm; (4) convert the hexidecimal SHA1
output to all lowercase. Only one <thread/> element MAY be
included in a message stanza, and it MUST NOT possess any
attributes. The <thread/> element MUST be treated as an opaque
string by entities; no semantic meaning may be derived from it,
and only exact, case-insensitve comparisons be made against it.
The <thread> element MUST NOT contain mixed content.
If the message stanza is of type "error", it MUST include an <error/>
child, which in turn MUST possess a 'code' attribute corresponding to
one of the standard error codes (Appendix A), MAY possess an
'xml:lang' attribute, and MAY also contain PCDATA corresponding to a
natural-language description of the error. An <error/> child MUST
NOT be included if the stanza type is anything other than "error".
An entity that receives a message stanza of type 'error' MUST NOT
respond to the stanza by sending a further message stanza of type
'error'; this helps to prevent looping.
7.4 Presence Stanzas
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 tex and optional user-defined descriptive
textt) and to communicate that status to other entities. They are
also used to negotiate and manage subscriptions to the presence of
other entities.
7.4.1 Types of Presence
The 'type' attribute of a presence stanza is optional. A presence
stanza that does not have a 'type' attribute is used to signal to the
server that the sender is online and available for communication. If
included, the 'type' attribute specifies the availability state of
the sender, a request to manage a subscription to another entity's
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presence, a request for another entity's current presence, or an
error related to a previously-sent presence stanza. The 'type'
attribute MAY 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. In general
SHOULD NOT be sent by a client.
o error -- An error has occurred regarding processing or delivery of
a previously-sent presence stanza.
Information about the subscription model used within XMPP can be
found in XMPP IM [3].
7.4.2 Children
As described under extended namespaces (Section 7.6), a presence
stanza MAY contain any properly-namespaced child element as long as
the namespace name is not "jabber:client", "jabber:server", or
"http://etherx.jabber.org/streams", and as long as the element name
does not match that of one of the core data elements, stream
elements, or defined children thereof.
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. Specifically, if a 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"):
o show -- Describes the availability status of an entity or specific
resource. Only one <show/> element MAY be included in a presence
stanza, and it MUST NOT possess any attributes. The value SHOULD
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be one of the following (values other than these four MAY be
ignored; additional availability types could be defined through a
properly-namespaced child element of the presence stanza):
* away -- The entity or resource is temporarily away.
* chat -- The entity or resource is actively interested in
chatting.
* xa -- The entity or resource is away for an extended period (xa
= "eXtended Away").
* dnd -- The entity or resource is busy (dnd = "Do Not Disturb").
o status -- An optional natural-language description of availability
status. Normally used in conjunction with the show element to
provide a detailed description of an availability state (e.g., "In
a meeting"). 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.
o priority -- An optional element specifying the priority level of
the connected resource. The value may be any integer between -128
to 127. Only one <priority/> element MAY be included in a
presence stanza, and it MUST NOT possess any attributes.
If the presence stanza is of type "error", it MUST include an <error/
> child, which in turn MUST possess a 'code' attribute corresponding
to one of the standard error codes (Appendix A) and MAY contain
PCDATA corresponding to a natural-language description of the error.
An <error/> child MUST NOT be included if the stanza type is anything
other than "error". An entity that receives a presence stanza of
type 'error' MUST NOT respond to the stanza by sending a further
presence stanza of type 'error'; this helps to prevent looping.
As described under extended namespaces (Section 7.6), a presence
stanza MAY also contain any properly-namespaced child element (other
than the core data elements, stream elements, or defined children
thereof).
7.5 IQ Stanzas
7.5.1 Overview
Info/Query, or IQ, is a request-response mechanism, similar in some
ways to HTTP [24]. IQ stanzas in the 'jabber:client' or
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'jabber:server' namespace 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,
which responding entities SHOULD return in any response.
Most IQ interactions follow a common pattern of structured data
exchange such as get/result or set/result (although an error may be
returned in response 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='result' id='2'> |
| <------------------------ |
| |
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
SHOULD preserve the 'id' attribute of the request). 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).
7.5.2 Types of IQ
The 'type' attribute of an IQ stanza is REQUIRED. The 'type'
attribute specifies a distinct step within a request-response
interaction. The value SHOULD be one of the following (all other
values MAY be ignored):
o get -- The stanza is a request for information.
o set -- The stanza provides required data, sets new values, or
replaces existing values.
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o result -- The stanza is a response to a successful get or set
request.
o error -- An error has occurred regarding processing or delivery of
a previously-sent get or set.
7.5.3 Children
As described under extended namespaces (Section 7.6), an IQ stanza
MAY contain any properly-namespaced child element as long as the
namespace name is not "jabber:client", "jabber"server", or "http://
etherx.jabber.org/streams", and as long as the element name does not
match that of one of the core data elements, stream elements, or
defined children thereof. However, an IQ stanza contains no children
in the 'jabber:client' or 'jabber:server' namespace since it is a
vessel for XML in another namespace.
If the IQ stanza is of type "error", it MUST include an <error/>
child, which in turn MUST possess a 'code' attribute corresponding to
one of the standard error codes (Appendix A) and MAY contain PCDATA
corresponding to a natural-language description of the error. An
<error/> child MUST NOT be included if the stanza type is anything
other than "error". An entity that receives an IQ stanza of type
'error' MUST NOT respond to the stanza by sending a further IQ stanza
of type 'error'; this helps to prevent looping.
7.6 Extended Namespaces
While the core data elements 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 core data elements
for the purpose of providing additional functionality. Thus a
message, presence, or IQ stanza MAY house one or more optional child
elements containing content that extends the meaning of the message
(e.g., an encrypted form of the message body). This child element
MAY be any element (other than the core data elements, stream
elements, or defined children thereof). The child element MUST
possess an 'xmlns' namespace declaration (other than the stream
namespace and the default namespace) that defines all data contained
within the child element.
Support for any given extended namespace is OPTIONAL on the part of
any implementation. If an entity does not understand such a
namespace, it MUST ignore the associated XML data (if the stanza is
being routed on to another entity, ignore means "pass it on
untouched"). If an entity receives an IQ stanza in a namespace it
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does not understand, the entity SHOULD return an IQ stanza of type
"error" with an error element of code 501 (Not Implemented). If an
entity receives a message or presence stanza that contains XML data
in an extended namespace it does not understand, the portion of the
stanza that is in the unknown namespace SHOULD be ignored. If an
entity receives a message stanza without a <body/> element but
containing only a child element bound by a namespace it does not
understand, it MUST ignore the entire stanza.
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8. XML Usage within XMPP
8.1 Namespaces
XML Namespaces [15] 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 XML to be structurally mixed with any
data element within XMPP.
Additionally, XMPP is more strict about namespace prefixes than the
XML namespace specification requires.
8.2 Validation
A server is not responsible for validating the XML elements forwarded
to a client; an implementation MAY choose to provide only validated
data elements but is NOT REQUIRED to do so. 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.
8.3 Character Encodings
Software implementing XML streams MUST support the UTF-8 (RFC 2279
[25]) and UTF-16 (RFC 2781 [26]) transformations of Universal
Character Set (ISO/IEC 10646-1 [27]) characters. Software MUST NOT
attempt to use any other encoding for transmitted data. The
encodings of the transmitted and received streams are independent.
Software MAY select either UTF-8 or UTF-16 for the transmitted
stream, and SHOULD deduce the encoding of the received stream as
described in the XML specification [1]. For historical reasons,
existing implementations MAY support UTF-8 only.
8.4 Inclusion of Text Declaration
An application MAY send a text declaration. Applications MUST follow
the rules in the XML specification [1] regarding the circumstances
under which a text declaration is included.
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9. IANA Considerations
The IANA registers "xmpp" as a GSSAPI [29] service name, as specified
in Section 6.1.3.
Additionally, the IANA registers "jabber-client" and "jabber-server"
as keywords for TCP ports 5222 and 5269 respectively.
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10. Internationalization Considerations
Usage of the 'xml:lang' attribute is described above. If a client
includes an 'xml:lang' attribute in a stanza, the server MUST NOT
modify or delete it.
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11. Security Considerations
11.1 Client-to-Server Communications
The TLS protocol for encrypting XML streams provides a reliable
mechanism for helping to ensure the privacy and data integrity of
data exchanged between two entities.
The SASL protocol for authenticating XML streams (defined under
Section 6.1 above) provides a reliable mechanism for validating that
a client connecting to a server is who it claims to be.
The IP address and method of access of clients MUST NOT be made
available by a server, nor are any connections other than the
original server connection required. This helps protect the client's
server from direct attack or identification by third parties.
End-to-end encryption of message bodies and presence status
information MAY be effected through use of the methods defined in
End-to-End Object Encryption in XMPP [28].
11.2 Server-to-Server Communications
It is OPTIONAL for any given server to communicate with other
servers, and server-to-server communications MAY be disabled by the
administrator of any given deployment.
If two servers would like to enable communications between
themselves, they MUST form a relationship of trust at some level,
either based on trust in DNS or based on a pre-existing trust
relationship (e.g., through exchange of certificates). If two
servers have a pre-existing trust relationship, they MAY use SASL
Authentication (Section 6.1) for the purpose of authenticating each
other. If they do not have a pre-existing relationship, they MUST
use the Dialback Protocol (Section 6.2), which provides a reliable
mechanism for preventing the spoofing of servers.
11.3 Firewalls
Communications using XMPP occur over TCP sockets on port 5222
(client-to-server) or port 5269 (server-to-server), as registered
with the IANA [7]. Use of these well-known ports allows
administrators to easily enable or disable XMPP activity through
existing and commonly-deployed firewalls.
11.4 Minimum Security Mechanisms
Although service provisioning is a policy matter, at a minimum, all
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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 (using the TLS_RSA_WITH_3DES_EDE_CBC_SHA cipher
supporting client-side certificates)
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References
[1] World Wide Web Consortium, "Extensible Markup Language (XML)
1.0 (Second Edition)", W3C xml, October 2000, <http://
www.w3.org/TR/2000/REC-xml-20001006>.
[2] Jabber Software Foundation, "Jabber Software Foundation",
August 2001, <http://www.jabber.org/>.
[3] Saint-Andre, P. and J. Miller, "XMPP Instant Messaging (draft-
ietf-xmpp-im-04, work in progress)", February 2003.
[4] Day, M., Aggarwal, S., Mohr, G. and J. Vincent, "A Model for
Presence and Instant Messaging", RFC 2779, February 2000,
<http://www.ietf.org/rfc/rfc2779.txt>.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[6] University of Southern California, "Transmission Control
Protocol", RFC 793, September 1981, <http://www.ietf.org/rfc/
rfc0793.txt>.
[7] Internet Assigned Numbers Authority, "Internet Assigned Numbers
Authority", January 1998, <http://www.iana.org/>.
[8] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998, <http://www.ietf.org/rfc/rfc2396.txt>.
[9] Harrenstien, K., Stahl, M. and E. Feinler, "DoD Internet host
table specification", RFC 952, October 1985.
[10] Braden, R., "Requirements for Internet Hosts - Application and
Support", STD 3, RFC 1123, October 1989.
[11] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep Profile
for Internationalized Domain Names (draft-ietf-idn-nameprep-11,
work in progress)", June 2002.
[12] Hoffman, P. and M. Blanchet, "Preparation of Internationalized
Strings ("stringprep")", RFC 3454, December 2002.
[13] Saint-Andre, P. and J. Hildebrand, "Nodeprep: A Stringprep
Profile for Node Identifiers in XMPP (draft-ietf-xmpp-nodeprep-
01, work in progress)", February 2003.
[14] Saint-Andre, P. and J. Hildebrand, "Resourceprep: A Stringprep
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Profile for Resource Identifiers in XMPP (draft-ietf-xmpp-
resourceprep-01, work in progress)", February 2003.
[15] World Wide Web Consortium, "Namespaces in XML", W3C xml-names,
January 1999, <http://www.w3.org/TR/1999/REC-xml-names-
19990114/>.
[16] Myers, J., "Simple Authentication and Security Layer (SASL)",
RFC 2222, October 1997.
[17] Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A. and
P. Kocher, "The TLS Protocol Version 1.0", RFC 2246, January
1999.
[18] Crispin, M., "Internet Message Access Protocol - Version
4rev1", RFC 2060, December 1996.
[19] Myers, J. and M. Rose, "Post Office Protocol - Version 3", STD
53, RFC 1939, May 1996.
[20] Newman, C. and J. Myers, "ACAP -- Application Configuration
Access Protocol", RFC 2244, November 1997.
[21] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC 2595,
June 1999.
[22] Alvestrand, H., "Tags for the Identification of Languages", BCP
47, RFC 3066, January 2001.
[23] Gulbrandsen, A. and P. Vixie, "A DNS RR for specifying the
location of services (DNS SRV)", RFC 2052, October 1996.
[24] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[25] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
2279, January 1998.
[26] Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO 10646",
RFC 2781, February 2000.
[27] 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.
[28] Saint-Andre, P. and J. Hildebrand, "End-to-End Object
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Encryption in XMPP (draft-ietf-xmpp-e2e-00, work in progress)",
February 2003.
[29] Linn, J., "Generic Security Service Application Program
Interface, Version 2", RFC 2078, January 1997.
Authors' Addresses
Peter Saint-Andre
Jabber Software Foundation
EMail: stpeter@jabber.org
URI: http://www.jabber.org/people/stpeter.php
Jeremie Miller
Jabber Software Foundation
EMail: jeremie@jabber.org
URI: http://www.jabber.org/people/jer.php
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Appendix A. Standard Error Codes
A standard error element is used for failed processing of XML stanzas
within the "jabber:client" or "jabber:server" namespace. This
element is a child of the failed stanza and MUST include a 'code'
attribute corresponding to an appropriate error condition.
In general the standard error codes were "borrowed" from those used
in HTTP [24] early in the development of XMPP within the Jabber
community. The first digit of the error code defines the class of
response. The last two digits do not have any categorization role.
There are five possible values for the first digit:
o 1xx: Informational - Request received, continuing process [not
currently used within XMPP]
o 2xx: Success - The action was successfully received, understood,
and accepted [not currently used within XMPP]
o 3xx: Redirection - Further action must be taken in order to
complete the request
o 4xx: Sender Error - The sender's request contains bad syntax or
cannot be fulfilled
o 5xx: Receiver Error - The receiving or routing entity (often but
not always a server) failed to fulfill an apparently valid request
The individual values of the numeric status/error codes defined for
XMPP, and an example set of corresponding textual descriptions, are
presented below. The textual descriptions listed here are only
recommendations -- they MAY be replaced by local equivalents without
affecting the protocol.
o 302 (Redirect) - Code 302 is used when a server needs to redirect
stream initiation requests to another hostname or IP address.
o 400 (Bad Request) - Code 400 is used to inform a sender that a
request could not be understood by the recipient. This might be
generated when an entity sends non-well-formed XML or when a
message stanza does not have a 'to' attribute.
o 401 (Unauthorized) - Code 401 is used to inform clients that they
have provided incorrect authorization information, e.g., an
incorrect password or unknown username when attempting to
authenticate with a service.
o 402 (Payment Required) - Code 402 is being reserved for future
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use.
o 403 (Forbidden) - Code 403 is used to inform an entity that its
request was understood but that the recipient is refusing to
fulfill it, e.g., if a user attempts to set information associated
with another user.
o 404 (Not Found) - Code 404 is used to inform a sender that no
recipient was found matching the JID to which an XML stanza was
sent, e.g., if a sender has attempted to send a message to a JID
that does not exist. (Note: if the server of the intended
recipient cannot be reached, an error code from the 500 series
must be sent.)
o 405 (Not Allowed) - Code 405 is used when the action requested is
not allowed for the JID identified by the 'from' address, e.g., if
a client attempts to set the time or version of a server.
o 406 (Not Acceptable) - Code 406 is used when an XML stanza is for
some reason not acceptable to a server or other entity. This
might be generated when, for example, a user attempts to register
with a service using an empty password.
o 407 (Registration Required) - Code 407 is used when a message or
request is sent to a service that requires prior registration,
e.g., if a user attempts to send a message through a gateway to a
foreign messaging system without having first registered with that
gateway.
o 408 (Request Timeout) - Code 408 is returned when a recipient does
not produce a response within the time that the sender was
prepared to wait.
o 409 (Conflict) - Code 409 is returned when a request cannot be
fulfilled because of an inherent conflict (e.g., because a client
attempts to authorize a resouce name that is already in use).
o 410 (Gone) - Code 410 is returned by a server when the hostname
requested by an entity initiating a stream request is no longer
provided by a server.
o 500 (Internal Server Error) - Code 500 is used when a server or
service encounters an unexpected condition which prevents it from
handling a stream initiation request or an XML stanza from a
sender.
o 501 (Not Implemented) - Code 501 is used when the recipient does
not support the functionality being requested by a sender, e.g.,
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if a user attempts to register with a server that does not allow
registration.
o 502 (Remote Server Error) - Code 502 is used when delivery of an
XML stanza fails because of an inability to reach the intended
remote server or service, e.g., because a remote server's hostname
could not be resolved.
o 503 (Service Unavailable) - Code 503 is used when a sender
requests a service that a recipient is temporarily unable to
offer.
o 504 (Remote Server Timeout) - Code 504 is used when attempts to
contact a remote server timeout, e.g., if an incorrect hostname is
specified.
o 505 (Version Not Supported) - Code 505 is used when a server does
not support the XMPP version requested by an entity that initiates
a stream to the server.
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Appendix B. XML Schemas
The following XML schemas are descriptive, not normative.
B.1 streams namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xsd='http://www.w3.org/2001/XMLSchema'
targetNamespace='http://etherx.jabber.org/streams'
xmlns='http://etherx.jabber.org/streams'
elementFormDefault='qualified'>
<xs:element name='stream'>
<xs:complexType>
<xs:element ref='features' minOccurs='0' maxOccurs='unbounded'/>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
<xs:choice>
<xs:any
namespace='jabber:client'
maxOccurs='1'/>
<xs:any
namespace='jabber:server'
maxOccurs='1'/>
</xs:choice>
<xs:attribute name='to' type='xs:string' use='optional'/>
<xs:attribute name='from' type='xs:string' use='optional'/>
<xs:attribute name='id' type='xs:ID' use='optional'/>
<xs:attribute name='version' type='xs:decimal' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='error'/>
<xs:complexType>
<xs:attribute name='code' type='xs:string' use='required'>
<xs:simpleType>
<xs:restriction base='xs:nonNegativeInteger'>
<xs:enumeration value='302'/>
<xs:enumeration value='400'/>
<xs:enumeration value='404'/>
<xs:enumeration value='410'/>
<xs:enumeration value='500'/>
<xs:enumeration value='505'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
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</xs:element>
</xs:schema>
B.2 SASL namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xsd='http://www.w3.org/2001/XMLSchema'
targetNamespace='http://www.iana.org/assignments/sasl-mechanisms'
xmlns='http://www.iana.org/assignments/sasl-mechanisms'
elementFormDefault='qualified'>
<xs:element name='mechanisms'>
<xs:complexType>
<xs:sequence minOccurs='0' maxOccurs='unbounded'>
<xs:element ref='mechanism'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='mechanism'/>
<xs:element name='auth'>
<xs:complexType>
<xs:attribute name='mechanism' type='xs:string' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='challenge' type='xs:string'/>
<xs:element name='response' type='xs:string'/>
<xs:element name='abort'/>
<xs:element name='success'/>
<xs:element name='failure'>
<xs:complexType>
<xs:attribute name='code' type='xs:string' use='optional'/>
</xs:complexType>
</xs:element>
</xs:schema>
B.3 Dialback namespace
<?xml version='1.0' encoding='UTF-8'?>
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<xs:schema
xmlns:xsd='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:string'>
<xs:attribute name='from' type='xs:string' use='required'/>
<xs:attribute name='to' type='xs:string' use='required'/>
<xs:attribute name='type' type='xs:string' 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:element name='verify'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute name='from' type='xs:string' use='required'/>
<xs:attribute name='to' type='xs:string' use='required'/>
<xs:attribute name='id' type='xs:string' use='required'/>
<xs:attribute name='type' type='xs:string' 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>
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B.4 jabber:client namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xsd='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:client'
xmlns='jabber:client'
elementFormDefault='qualified'>
<xs:element name='message'>
<xs:complexType>
<xs:choice maxOccurs='unbounded'>
<xs:element ref='body' minOccurs='0' maxOccurs='unbounded'/>
<xs:element ref='subject' minOccurs='0' maxOccurs='unbounded'/>
<xs:element ref='thread' minOccurs='0' maxOccurs='1'/>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:choice>
<xs:attribute name='to' type='xs:string' use='optional'/>
<xs:attribute name='from' type='xs:string' use='optional'/>
<xs:attribute name='id' type='xs:ID' use='optional'/>
<xs:attribute name='xml:lang' type='xs:NMTOKEN' use='optional'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='chat'/>
<xs:enumeration value='groupchat'/>
<xs:enumeration value='headline'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='body' type='xs:string'>
<xs:complexType>
<xs:attribute name='xml:lang' type='xs:NMTOKEN' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='subject' type='xs:string'>
<xs:complexType>
<xs:attribute name='xml:lang' type='xs:NMTOKEN' use='optional'/>
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</xs:complexType>
</xs:element>
<xs:element name='thread' type='xs:string'/>
<xs:element name='presence'>
<xs:complexType>
<xs:choice maxOccurs='unbounded'>
<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:element ref='error' minOccurs='0' maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:choice>
<xs:attribute name='to' type='xs:string' use='optional'/>
<xs:attribute name='from' type='xs:string' use='optional'/>
<xs:attribute name='id' type='xs:ID' use='optional'/>
<xs:attribute name='xml:lang' type='xs:NMTOKEN' 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='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</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='xa'/>
<xs:enumeration value='dnd'/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name='status' type='xs:string'>
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<xs:complexType>
<xs:attribute name='xml:lang' type='xs:NMTOKEN' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='priority' type='xs:byte'/>
<xs:element name='iq'>
<xs:complexType>
<xs:choice maxOccurs='unbounded'>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:choice>
<xs:attribute name='to' type='xs:string' use='optional'/>
<xs:attribute name='from' type='xs:string' use='optional'/>
<xs:attribute name='id' type='xs:ID' 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:complexType>
</xs:element>
<xs:element name='error'>
<xs:complexType>
<xs:attribute
name='code'
type='xs:nonNegativeInteger'
use='required'/>
<xs:attribute name='xml:lang' type='xs:NMTOKEN' use='optional'/>
</xs:complexType>
</xs:element>
</xs:schema>
B.5 jabber:server namespace
<?xml version='1.0' encoding='UTF-8'?>
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<xs:schema
xmlns:xsd='http://www.w3.org/2001/XMLSchema'
targetNamespace='http://www.jabber.org/protocol'
xmlns='http://www.jabber.org/protocol'
elementFormDefault='qualified'>
<xs:element name='message'>
<xs:complexType>
<xs:choice maxOccurs='unbounded'>
<xs:element ref='body' minOccurs='0' maxOccurs='unbounded'/>
<xs:element ref='subject' minOccurs='0' maxOccurs='unbounded'/>
<xs:element ref='thread' minOccurs='0' maxOccurs='1'/>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:choice>
<xs:attribute name='to' type='xs:string' use='required'/>
<xs:attribute name='from' type='xs:string' use='required'/>
<xs:attribute name='id' type='xs:ID' use='optional'/>
<xs:attribute name='xml:lang' type='xs:NMTOKEN' use='optional'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='chat'/>
<xs:enumeration value='groupchat'/>
<xs:enumeration value='headline'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='body' type='xs:string'>
<xs:complexType>
<xs:attribute name='xml:lang' type='xs:NMTOKEN' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='subject' type='xs:string'>
<xs:complexType>
<xs:attribute name='xml:lang' type='xs:NMTOKEN' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='thread' type='xs:string'/>
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<xs:element name='presence'>
<xs:complexType>
<xs:choice maxOccurs='unbounded'>
<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:element ref='error' minOccurs='0' maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:choice>
<xs:attribute name='to' type='xs:string' use='required'/>
<xs:attribute name='from' type='xs:string' use='required'/>
<xs:attribute name='id' type='xs:ID' use='optional'/>
<xs:attribute name='xml:lang' type='xs:NMTOKEN' 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='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</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='xa'/>
<xs:enumeration value='dnd'/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name='status' type='xs:string'>
<xs:complexType>
<xs:attribute name='xml:lang' type='xs:NMTOKEN' use='optional'/>
</xs:complexType>
</xs:element>
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<xs:element name='priority' type='xs:byte'/>
<xs:element name='iq'>
<xs:complexType>
<xs:choice maxOccurs='unbounded'>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:choice>
<xs:attribute name='to' type='xs:string' use='required'/>
<xs:attribute name='from' type='xs:string' use='required'/>
<xs:attribute name='id' type='xs:ID' 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:complexType>
</xs:element>
<xs:element name='error'>
<xs:complexType>
<xs:attribute
name='code'
type='xs:nonNegativeInteger'
use='required'/>
<xs:attribute name='xml:lang' type='xs:NMTOKEN' use='optional'/>
</xs:complexType>
</xs:element>
</xs:schema>
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Appendix C. Revision History
Note to RFC editor: please remove this entire appendix, and the
corresponding entries in the table of contents, prior to publication.
C.1 Changes from draft-ietf-xmpp-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.
C.2 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".
C.3 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.
o Corrected error in Stream Authentication regarding "version='1.0'"
flag.
o Made numerous small editorial changes.
C.4 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.
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o Made numerous small editorial fixes.
C.5 Changes from draft-miller-xmpp-core-02
o Brought Streams Authentication 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.
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 types and the <thread/> element in message stanzas.
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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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Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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