One document matched: draft-saintandre-rfc3920bis-03.txt
Differences from draft-saintandre-rfc3920bis-02.txt
Network Working Group P. Saint-Andre, Ed.
Internet-Draft XMPP Standards Foundation
Obsoletes: 3920 (if approved) July 17, 2007
Intended status: Standards Track
Expires: January 18, 2008
Extensible Messaging and Presence Protocol (XMPP): Core
draft-saintandre-rfc3920bis-03
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document defines the core features of the Extensible Messaging
and Presence Protocol (XMPP), a technology for streaming Extensible
Markup Language (XML) elements in order to exchange structured
information in close to real time between any two network-aware
entities. XMPP provides a generalized, extensible framework for
incrementally exchanging XML data, upon which a variety of
applications can be built. The framework includes methods for stream
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setup and teardown, channel encryption, authentication of a client to
a server and of one server to another server, and primitives for
push-style messages, publication of network availability information
("presence"), and request-response interactions between any two XMPP
entities. This document also specifies the format for XMPP
addresses, which are fully internationalizable.
This document obsoletes RFC 3920.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Functional Summary . . . . . . . . . . . . . . . . . . . 5
1.3. Conventions . . . . . . . . . . . . . . . . . . . . . . 7
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Server . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3. Client . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.4. Network . . . . . . . . . . . . . . . . . . . . . . . . 9
3. Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2. Domain Identifier . . . . . . . . . . . . . . . . . . . 10
3.3. Node Identifier . . . . . . . . . . . . . . . . . . . . 11
3.4. Resource Identifier . . . . . . . . . . . . . . . . . . 11
3.5. Determination of Addresses . . . . . . . . . . . . . . . 12
4. TCP Binding . . . . . . . . . . . . . . . . . . . . . . . . . 12
5. XML Streams . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 13
5.2. Stream Security . . . . . . . . . . . . . . . . . . . . 15
5.3. Stream Attributes . . . . . . . . . . . . . . . . . . . 16
5.4. Namespace Declarations . . . . . . . . . . . . . . . . . 22
5.5. Stream Features . . . . . . . . . . . . . . . . . . . . 22
5.6. Closing Streams . . . . . . . . . . . . . . . . . . . . 23
5.7. Reconnection . . . . . . . . . . . . . . . . . . . . . . 24
5.8. Stream Errors . . . . . . . . . . . . . . . . . . . . . 24
5.9. Simplified Stream Examples . . . . . . . . . . . . . . . 41
6. STARTTLS Negotiation . . . . . . . . . . . . . . . . . . . . 43
6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 43
6.2. Rules . . . . . . . . . . . . . . . . . . . . . . . . . 44
6.3. Process . . . . . . . . . . . . . . . . . . . . . . . . 44
6.4. Representation of JIDs in Certificates . . . . . . . . . 48
7. SASL Negotiation . . . . . . . . . . . . . . . . . . . . . . 49
7.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 49
7.2. Rules . . . . . . . . . . . . . . . . . . . . . . . . . 49
7.3. Process . . . . . . . . . . . . . . . . . . . . . . . . 51
7.4. SASL Definition . . . . . . . . . . . . . . . . . . . . 56
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7.5. SASL Errors . . . . . . . . . . . . . . . . . . . . . . 57
8. Resource Binding . . . . . . . . . . . . . . . . . . . . . . 60
8.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 60
8.2. Advertising Support . . . . . . . . . . . . . . . . . . 60
8.3. Server-Generated Resource Identifier . . . . . . . . . . 61
8.4. Client-Generated Resource Identifier . . . . . . . . . . 62
8.5. Binding Multiple Resources . . . . . . . . . . . . . . . 64
9. XML Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 67
9.1. Common Attributes . . . . . . . . . . . . . . . . . . . 67
9.2. Basic Semantics . . . . . . . . . . . . . . . . . . . . 71
9.3. Stanza Errors . . . . . . . . . . . . . . . . . . . . . 73
9.4. Extended Content . . . . . . . . . . . . . . . . . . . . 88
10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 89
10.1. Client-to-Server . . . . . . . . . . . . . . . . . . . . 89
10.2. Server-to-Server Examples . . . . . . . . . . . . . . . 95
11. Server Rules for Processing XML Stanzas . . . . . . . . . . . 99
11.1. No 'to' Address . . . . . . . . . . . . . . . . . . . . 99
11.2. Local Domain . . . . . . . . . . . . . . . . . . . . . . 100
11.3. Resource at Local Domain . . . . . . . . . . . . . . . . 100
11.4. Node at Local Domain . . . . . . . . . . . . . . . . . . 101
11.5. Foreign Domain . . . . . . . . . . . . . . . . . . . . . 101
12. XML Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 102
12.1. Restrictions . . . . . . . . . . . . . . . . . . . . . . 102
12.2. XML Namespace Names and Prefixes . . . . . . . . . . . . 103
12.3. Validation . . . . . . . . . . . . . . . . . . . . . . . 105
12.4. Inclusion of Text Declaration . . . . . . . . . . . . . 106
12.5. Character Encoding . . . . . . . . . . . . . . . . . . . 106
12.6. White Space . . . . . . . . . . . . . . . . . . . . . . 106
13. Compliance Requirements . . . . . . . . . . . . . . . . . . . 106
13.1. Servers . . . . . . . . . . . . . . . . . . . . . . . . 107
13.2. Clients . . . . . . . . . . . . . . . . . . . . . . . . 107
14. Internationalization Considerations . . . . . . . . . . . . . 107
15. Security Considerations . . . . . . . . . . . . . . . . . . . 108
15.1. High Security . . . . . . . . . . . . . . . . . . . . . 108
15.2. Certificate Validation . . . . . . . . . . . . . . . . . 108
15.3. Client-to-Server Communication . . . . . . . . . . . . . 109
15.4. Server-to-Server Communication . . . . . . . . . . . . . 110
15.5. Order of Layers . . . . . . . . . . . . . . . . . . . . 110
15.6. Lack of SASL Channel Binding to TLS . . . . . . . . . . 110
15.7. Mandatory-to-Implement Technologies . . . . . . . . . . 111
15.8. Firewalls . . . . . . . . . . . . . . . . . . . . . . . 111
15.9. Use of base64 in SASL . . . . . . . . . . . . . . . . . 111
15.10. Stringprep Profiles . . . . . . . . . . . . . . . . . . 111
15.11. Address Spoofing . . . . . . . . . . . . . . . . . . . . 112
15.12. Denial of Service . . . . . . . . . . . . . . . . . . . 114
15.13. Presence Leaks . . . . . . . . . . . . . . . . . . . . . 115
15.14. Directory Harvesting . . . . . . . . . . . . . . . . . . 116
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 116
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16.1. XML Namespace Name for TLS Data . . . . . . . . . . . . 116
16.2. XML Namespace Name for SASL Data . . . . . . . . . . . . 116
16.3. XML Namespace Name for Stream Errors . . . . . . . . . . 116
16.4. XML Namespace Name for Resource Binding . . . . . . . . 117
16.5. XML Namespace Name for Stanza Errors . . . . . . . . . . 117
16.6. Nodeprep Profile of Stringprep . . . . . . . . . . . . . 117
16.7. Resourceprep Profile of Stringprep . . . . . . . . . . . 118
16.8. GSSAPI Service Name . . . . . . . . . . . . . . . . . . 118
16.9. Port Numbers . . . . . . . . . . . . . . . . . . . . . . 118
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 118
17.1. Normative References . . . . . . . . . . . . . . . . . . 118
17.2. Informative References . . . . . . . . . . . . . . . . . 120
Appendix A. Nodeprep . . . . . . . . . . . . . . . . . . . . . . 124
A.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 124
A.2. Character Repertoire . . . . . . . . . . . . . . . . . . 124
A.3. Mapping . . . . . . . . . . . . . . . . . . . . . . . . 124
A.4. Normalization . . . . . . . . . . . . . . . . . . . . . 124
A.5. Prohibited Output . . . . . . . . . . . . . . . . . . . 125
A.6. Bidirectional Characters . . . . . . . . . . . . . . . . 125
Appendix B. Resourceprep . . . . . . . . . . . . . . . . . . . . 125
B.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 125
B.2. Character Repertoire . . . . . . . . . . . . . . . . . . 126
B.3. Mapping . . . . . . . . . . . . . . . . . . . . . . . . 126
B.4. Normalization . . . . . . . . . . . . . . . . . . . . . 126
B.5. Prohibited Output . . . . . . . . . . . . . . . . . . . 126
B.6. Bidirectional Characters . . . . . . . . . . . . . . . . 127
Appendix C. XML Schemas . . . . . . . . . . . . . . . . . . . . 127
C.1. Streams namespace . . . . . . . . . . . . . . . . . . . 127
C.2. Stream error namespace . . . . . . . . . . . . . . . . . 128
C.3. TLS namespace . . . . . . . . . . . . . . . . . . . . . 131
C.4. SASL namespace . . . . . . . . . . . . . . . . . . . . . 131
C.5. Resource binding namespace . . . . . . . . . . . . . . . 133
C.6. Stanza error namespace . . . . . . . . . . . . . . . . . 135
Appendix D. Contact Addresses . . . . . . . . . . . . . . . . . 136
Appendix E. Account Provisioning . . . . . . . . . . . . . . . . 137
Appendix F. Differences From RFC 3920 . . . . . . . . . . . . . 137
Appendix G. Copying Conditions . . . . . . . . . . . . . . . . . 138
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 139
Intellectual Property and Copyright Statements . . . . . . . . . 140
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1. Introduction
1.1. Overview
The Extensible Messaging and Presence Protocol (XMPP) is an
Extensible Markup Language [XML] technology for near-real-time
messaging, presence, and request-response services. The basic syntax
and semantics were developed originally within the Jabber open-source
community, mainly in 1999. In late 2002, the XMPP Working Group was
chartered with developing an adaptation of the core Jabber protocol
that would be suitable as an IETF instant messaging (IM) and presence
technology. As a result of work by the XMPP WG, [RFC3920] was
published in October 2004.
As a result of extensive implementation and deployment experience
with XMPP since that time, as well as more formal interoperability
testing, this document reflects consensus from the XMPP developer
community regarding XMPP's core XML streaming technology. In
particular, this document incorporates the following backward-
compatible changes from RFC 3920:
o Corrections and errata
o Additional examples throughout
o Clarifications and more complete specification of matters that
were underspecified
o Modifications to reflect updated technologies for which XMPP is a
using protocol (e.g., Transport Layer Security and the Simple
Authentication and Security Layer)
o Definition of several additional error conditions
o Addition of TLS plus SASL PLAIN as a mandatory-to-implement
technology
o Definition of optional support for multiple resources over the
same connection
o Removal of historical documentation for the server dialback
protocol from this specification to a separate specification
Therefore, this document defines the core features of XMPP 1.0 and
obsoletes RFC 3920.
Note: The XMPP extensions required to provide the basic instant
messaging and presence functionality defined in [IMP-REQS] are
specified in [XMPP-IM].
1.2. Functional Summary
This non-normative section provides a developer-friendly, functional
summary of XMPP; refer to the sections that follow for a normative
definition of XMPP.
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The purpose of XMPP is to enable the exchange of relatively small
pieces of structured data (called "XML stanzas") over a network
between any two (or more) entities. XMPP is implemented using a
client-server architecture, wherein a client must connect to a server
in order to gain access to the network and thus be allowed to
exchange XML stanzas with other entities. The process whereby a
client connects to a server, exchanges XML stanzas, and ends the
connection is:
1. Determine the hostname and port at which to connect
2. Open a TCP connection
3. Open an XML stream
4. Complete TLS negotiation for channel encryption (recommended)
5. Complete SASL negotiation for authentication
6. Bind a resource to the stream
7. Exchange an unbounded number of XML stanzas with other entities
on the network
8. Close the XML stream
9. Close the TCP connection
In the sections following discussion of XMPP architecture and XMPP
addresses, this document specifies how clients connect to servers and
specifies the basic semantics of XML stanzas. However, this document
does not define the "payloads" of the XML stanzas that might be
exchanged once a connection is successfully established; instead,
definition of such semantics is provided by XMPP extensions (e.g.,
[XMPP-IM] defines extensions for basic instant messaging and presence
functionality, and various specifications produced in the XMPP
Standards Foundation's XEP series define extensions for a wide range
of more advanced functionality).
Within the client-server architecture used by XMPP, one server may
optionally connect to another server to enable inter-domain or inter-
server communication. For this to happen, the two servers must
negotiate a connection between themselves and then exchange XML
stanzas; the process for doing so is:
1. Determine the hostname and port at which to connect
2. Open a TCP connection
3. Open an XML stream
4. Complete TLS negotiation for channel encryption (recommended)
5. Complete SASL negotiation for authentication
6. Exchange an unbounded number of XML stanzas both directly for the
servers and indirectly on behalf of entities associated with each
server (e.g., connected clients)
7. Close the XML stream
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8. Close the TCP connection
Note: Depending on local service policies, a service may wish to use
the older server dialback protocol to provide weak identity
verification in cases where SASL negotiation would not result in
strong authentication (e.g., because the certificate presented by the
peer service during TLS negotiation is self-signed and thus provides
only weak identity); for details, see [XEP-0220].
1.3. Conventions
The following keywords are to be interpreted as described in [TERMS]:
"MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD",
"RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
In examples, lines have been wrapped for improved readability,
"[...]" means elision, and the following prepended strings are used:
o C: = client
o E: = any XMPP entity
o I: = initiating entity
o P: = peer server
o R: = receiving entity
o S: = server
o S1: = server1
o S2: = server2
2. Architecture
2.1. Overview
XMPP assumes a client-server architecture, wherein a client utilizing
XMPP accesses a server (normally over a [TCP] connection) and servers
can also communicate with each other over TCP connections.
A simplified architectural diagram for a typical deployment is shown
here, where the entities have the following significance:
o romeo@example.net -- an XMPP user.
o example.net -- an XMPP server.
o example.com -- an XMPP server.
o juliet@example.com -- an XMPP user.
example.net -------------------- example.com
| |
| |
romeo@example.net juliet@example.com
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Note: Architectures that employ the syntax of XML stanzas (Section 9)
but that establish peer-to-peer connections directly between clients
using technologies based on [LINKLOCAL] have been deployed, but such
architectures are not XMPP and are best described as "XMPP-like"; for
details, see [XEP-0174].
2.2. Server
A SERVER is an entity whose primary responsibilities are to:
o Manage XML streams (Section 5) with local clients and deliver XML
stanzas (Section 9) to those clients over the negotiated XML
streams.
o Subject to local service policies on server-to-server
communication, manage XML streams (Section 5) with foreign servers
and route XML stanzas (Section 9) to those servers over the
negotiated XML streams.
Depending on the application, the secondary responsibilities of an
XMPP server may include:
o Storing XML data that is used by clients (e.g., contact lists for
users of XMPP-based instant messaging and presence applications);
in this case, the relevant XML stanza is handled directly by the
server itself on behalf of the client and is not routed to a
foreign server or delivered to a local entity.
o Hosting local services that also use XMPP as the basis for
communication but that provide additional functionality beyond
that defined in this document or in [XMPP-IM]; examples include
multi-user conferencing services as specified in [XEP-0045] and
publish-subscribe services as specified in [XEP-0060].
2.3. Client
A CLIENT is an entity that establiishes an XML stream with a server
by authenticating using the credentials of a local account and that
then completes resource binding (Section 8) in order to enable
delivery of XML stanzas via the server to the client. A client then
uses XMPP to communicate with its server, other clients, and any
other accessible entities on a network. Multiple clients may connect
simultaneously to a server on behalf of a local account, with each
client differentiated by the resource identifier portion of an XMPP
address (e.g., <node@domain/home> vs. <node@domain/work>), as defined
under Section 3 and Section 8. The RECOMMENDED port for TCP
connections between a client and a server is 5222, as registered with
the IANA (see Section 16.9).
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2.4. Network
Because each server is identified by a network address and because
server-to-server communication is a straightforward extension of the
client-to-server protocol, in practice the system consists of a
network of servers that inter-communicate. Thus, for example,
<juliet@example.com> is able to exchange messages, presence, and
other information with <romeo@example.net>. This pattern is familiar
from messaging protocols (such as [SMTP]) that make use of network
addressing standards. Communication between any two servers is
OPTIONAL. If enabled, such communication SHOULD occur over XML
streams that are bound to [TCP] connections. The RECOMMENDED port
for tCP connections between servers is 5269, as registered with the
IANA (see Section 16.9.
3. Addresses
3.1. Overview
An ENTITY is anything that is network-addressable and that can
communicate using XMPP. For historical reasons, the native address
of an XMPP entity is called a JABBER IDENTIFIER or JID. A valid JID
contains a set of ordered elements formed of an XMPP domain
identifier, node identifier, and resource identifier.
The syntax for a JID is defined as follows using the Augmented
Backus-Naur Form as specified in [ABNF].
jid = [ node "@" ] domain [ "/" resource ]
node = 1*(nodepoint)
; a "nodepoint" is a UTF-8 encoded Unicode code
; point that satisfies the Nodeprep profile of
; stringprep
domain = fqdn / address-literal / idnlabel
fqdn = (idnlabel 1*("." idnlabel))
; an "idnlabel" is an internationalized label
; as described in RFC 3490
address-literal = IPv4address / IPv6address
; the "IPv4address" and "IPv6address" rules are
; defined in Appendix B of RFC 3513
resource = 1*(resourcepoint)
; a "resourcepoint" is a UTF-8 encoded Unicode
; code point that satisfies the Resourceprep
; profile of stringprep
All JIDs are based on the foregoing structure. One common use of
this structure is to identify a messaging and presence account, the
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server that hosts the account, and a connected resource (e.g., a
specific device) in the form of <node@domain/resource>. However,
node types other than clients are possible; for example, a specific
chat room offered by a multi-user conference service (see [XEP-0045])
could be addressed as <room@service> (where "room" is the name of the
chat room and "service" is the hostname of the multi-user conference
service) and a specific occupant of such a room could be addressed as
<room@service/nick> (where "nick" is the occupant's room nickname).
Many other JID types are possible (e.g., <domain/resource> could be a
server-side script or service).
Each allowable portion of a JID (node identifier, domain identifier,
and resource identifier) MUST NOT be more than 1023 bytes in length,
resulting in a maximum total size (including the '@' and '/'
separators) of 3071 bytes.
Note: While the format of a JID is consistent with [URI], an entity's
address on an XMPP network MUST be a JID (without a URI scheme) and
not a [URI] or [IRI] as specified in [XMPP-URI]; the latter
specification is provided only for use by non-XMPP applications.
3.2. Domain Identifier
The DOMAIN IDENTIFIER portion of a JID is that portion after the '@'
character (if any) and before the '/' character (if any); it is the
primary identifier and is the only REQUIRED element of a JID (a mere
domain identifier is a valid JID). Typically a domain identifier
identifies the "home" server to which clients connect for XML routing
and data management functionality. (Note: A single server may host
multiple domain identifiers, i.e., multiple local domains.) However,
it is not necessary for an XMPP domain identifier to identify an
entity that provides core XMPP server functionality (e.g., a domain
identifier may identity an entity such as a multi-user conference
service, a publish-subscribe service, or a user directory).
The domain identifier for every server or service that will
communicate over a network SHOULD be a fully qualified domain name
(see [DNS]) but MAY be either an IPv4 or IPv6 address or a text label
(commonly called an "unqualified hostname") that is resolvable on a
local network. If the domain identifier includes a final character
considered to be a label separator (dot) by [IDNA] or [STD13], this
character MUST be stripped from the domain identifier before the JID
of which it is a part is used for the purpose of routing an XML
stanza, comparing against another JID, or constructing an [XMPP-URI];
in particular, the character should be stripped before any other
canonicalization steps are taken (such as application of the
[NAMEPREP] profile of [STRINGPREP] or completion of the ToASCII
operation as described in [IDNA]).
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A domain identifier MUST be an "internationalized domain name" as
defined in [IDNA], that is, "a domain name in which every label is an
internationalized label". When preparing a text label (consisting of
a sequence of Unicode code points) for representation as an
internationalized label in the process of constructing an XMPP domain
identifier or comparing two XMPP domain identifiers, an application
MUST ensure that for each text label it is possible to apply without
failing the ToASCII operation specified in [IDNA] with the
UseSTD3ASCIIRules flag set (thus forbidding ASCII code points other
than letters, digits, and hyphens). If the ToASCII operation can be
applied without failing, then the label is an internationalized
label. An internationalized domain name (and therefore an XMPP
domain identifier) is constructed from its constituent
internationalized labels by following the rules specified in [IDNA].
(Note: The ToASCII operation includes application of the [NAMEPREP]
profile of [STRINGPREP] and encoding using the algorithm specified in
[PUNYCODE]; for details, see [IDNA].)
3.3. Node Identifier
The NODE IDENTIFIER portion of a JID is an optional secondary
identifier placed before the domain identifier and separated from the
latter by the '@' character. Typically a node identifier uniquely
identifies the entity requesting and using network access provided by
a server (i.e., a local account), although it can also represent
other kinds of entities (e.g., a chat room associated with a multi-
user conference service). The entity represented by an XMPP node
identifier is addressed within the context of a specific domain.
When the domain is an XMPP server and the entity is a local account
on the server, the resulting address (of the form <node@domain>) is
called a BARE JID.
A node identifier MUST be formatted such that the Nodeprep profile of
[STRINGPREP] can be applied without failing (see Appendix A). Before
comparing two node identifiers, an application MUST first apply the
Nodeprep profile to each identifier.
3.4. Resource Identifier
The RESOURCE IDENTIFIER portion of a JID is an optional tertiary
identifier placed after the domain identifier and separated from the
latter by the '/' character. A resource identifier may modify either
a <node@domain> address or a mere <domain> address. Typically a
resource identifier uniquely identifies a specific connection (e.g.,
a device or location) or object (e.g., a participant in a multi-user
conference room) belonging to the entity associated with an XMPP node
identifier at a local domain. A resource identifier has no semantic
meaning and is opaque to both servers and clients. A resource
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identifier is negotiated between a client and a server during
resource binding (Section 8), after which the entity is referred to
as a CONNECTED RESOURCE and its address (of the form
<node@domain/resource>) is referred to as a FULL JID. An entity MAY
maintain multiple connected resources simultaneously, with each
connected resource differentiated by a distinct resource identifier.
A resource identifier MUST be formatted such that the Resourceprep
profile of [STRINGPREP] can be applied without failing (see
Appendix B). Before comparing two resource identifiers, an
application MUST first apply the Resourceprep profile to each
identifier.
3.5. Determination of Addresses
After SASL negotiation (Section 7) and, if appropriate, resource
binding (Section 8), the receiving entity for a stream MUST determine
the initiating entity's JID.
For server-to-server communication, the initiating entity's JID
SHOULD be the authorization identity, derived from the authentication
identity (as defined by [SASL]), if no authorization identity was
specified during SASL negotiation (Section 7).
For client-to-server communication, the bare JID (<node@domain>)
SHOULD be the authorization identity, derived from the authentication
identity (as defined by [SASL]), if no authorization identity was
specified during SASL negotiation (Section 7); the resource
identifier portion of the full JID (<node@domain/resource>) SHOULD be
the resource identifier negotiated by the client and server during
resource binding (Section 8).
The receiving entity MUST ensure that the resulting JID (including
node identifier, domain identifier, resource identifier, and
separator characters) conforms to the rules and formats defined
earlier in this section; to meet this restriction, the receiving
entity may need to replace the JID sent by the initiating entity with
the canonicalized JID as determined by the receiving entity.
4. TCP Binding
As XMPP is defined herein, an initiating entity (client or server)
MUST open a TCP connection at the receiving entity (server) before it
negotiates XML streams with the receiving entity. However, prior to
opening the TCP connection, the initiating entity first MUST resolve
the Domain Name System (DNS) hostname associated with the receiving
entity and determine the appropriate TCP port for communication with
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the receiving entity. The process is:
1. Attempt to resolve the hostname using a [DNS-SRV] Service of
"xmpp-client" (for client-to-server connections) or "xmpp-server"
(for server-to-server connections) and Proto of "tcp", resulting
in resource records such as "_xmpp-client._tcp.example.com." or
"_xmpp-server._tcp.example.com."; the IP address and port at
which the initiating entity attempts to connect to the receiving
entity shall be those specified in the SRV lookup result.
2. If the SRV lookup fails, the fallback SHOULD be a normal IPv4 or
[IPv6] address record resolution to determine the IP address,
where the port used is the "xmpp-client" port of 5222 for client-
to-server connections or the "xmpp-server" port 5269 for server-
to-server connections.
3. For client-to-server connections, the fallback MAY be a [DNS-TXT]
lookup for alternative connection methods, for example as
described in [XEP-0156].
TCP connections are handled differently in client-to-server
communication and server-to-server ommunication. Specifically:
o Because a client is subordinate to a server and therefore a client
authenticates to the server but the server does not authenticate
to the client, it is necessary to have only one TCP connection
between client and server. Thus the server MUST allow the client
to share a single TCP connection for XML stanzas sent from client
to server and from server to client (i.e., the inital stream and
response stream as specified under Section 5).
o Because two servers are peers and therefore each peer must
authenticate with the other, the servers MUST use two TCP
connections: one for XML stanzas sent from the first server to the
second server and another (initiated by the second server) for
stanzas from the second server to the first server.
Note: There is no necessary coupling of an XML stream to a [TCP]
connection. For example, two entities could connect to each other
via another transport, such as [HTTP] as specified in [XEP-0124] and
[XEP-0206]. However, this specification defines a binding of XMPP to
TCP only.
5. XML Streams
5.1. Overview
Two fundamental concepts make possible the rapid, asynchronous
exchange of relatively small payloads of structured information
between presence-aware entities: XML streams and XML stanzas. These
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terms are defined as follows.
Definition of XML Stream: An XML STREAM is a container for the
exchange of XML elements between any two entities over a network.
The start of an XML stream is denoted unambiguously by an opening
XML <stream> tag (with appropriate attributes and namespace
declarations), while the end of the XML stream is denoted
unambiguously by a closing XML </stream> tag. During the life of
the stream, the entity that initiated it can send an unbounded
number of XML elements over the stream, either elements used to
negotiate the stream (e.g., to complete TLS negotiation
(Section 6) or SASL negotiation (Section 7)) or XML stanzas. The
INITIAL STREAM is negotiated from the initiating entity (typically
a client or server) to the receiving entity (typically a server),
and can be seen as corresponding to the initiating entity's
"connection" or "session" with the receiving entity. The initial
stream enables unidirectional communication from the initiating
entity to the receiving entity; in order to enable information
exchange from the receiving entity to the initiating entity, the
receiving entity MUST negotiate a stream in the opposite direction
(the RESPONSE STREAM).
Definition of XML Stanza: An XML STANZA is a discrete semantic unit
of structured information that is sent from one entity to another
over an XML stream, and is the basic unit of meaning in XMPP. An
XML stanza exists at the direct child level of the root <stream/>
element and is said to be well-balanced if it matches the
production [43] content of [XML]. The start of any XML stanza is
denoted unambiguously by the element start tag at depth=1 of the
XML stream (e.g., <presence>), and the end of any XML stanza is
denoted unambiguously by the corresponding close tag at depth=1
(e.g., </presence>); a server MUST NOT process a partial stanza
and MUST NOT attach meaning to the transmission timing of any part
of a stanza (before receipt of the close tag). The only XML
stanzas defined herein are the <message/>, <presence/>, and <iq/>
elements qualified by the default namespace for the stream, as
described under Section 9; an XML element sent for the purpose of
TLS negotiation (Section 6) or SASL negotiation (Section 7) is not
considered to be an XML stanza. An XML stanza MAY contain child
elements (with accompanying attributes, elements, and XML
character data) as necessary in order to convey the desired
information, which MAY be qualified by any XML namespace (see
[XML-NAMES] as well as Section 9.4 herein).
Consider the example of a client's connection to a server. In order
to connect to a server, a client MUST initiate an XML stream by
sending an opening <stream> tag to the server, optionally preceded by
a text declaration specifying the XML version and the character
encoding supported (see Section 12.4 and Section 12.5). Subject to
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local policies and service provisioning, the server SHOULD then reply
with a second XML stream back to the client, again optionally
preceded by a text declaration. Once the client has completed SASL
negotiation (Section 7) and resource binding (Section 8), the client
MAY send an unbounded number of XML stanzas over the stream to any.
When the client desires to close the stream, it simply sends a
closing </stream> tag to the server (see Section 5.6).
In essence, then, an XML stream acts as an envelope for all the XML
stanzas sent during a connection. We can represent this in a
simplistic fashion as follows.
+--------------------+
| <stream> |
|--------------------|
| <presence> |
| <show/> |
| </presence> |
|--------------------|
| <message to='foo'> |
| <body/> |
| </message> |
|--------------------|
| <iq to='bar'> |
| <query/> |
| </iq> |
|--------------------|
| [ ... ] |
|--------------------|
| </stream> |
+--------------------+
Note: Those who are accustomed to thinking of XML in a document-
centric manner may wish to view a client's connection to a server as
consisting of two open-ended XML documents: one from the client to
the server and one from the server to the client. From this
perspective, the root <stream/> element can be considered the
document entity for each "document", and the two "documents" are
built up through the accumulation of XML stanzas sent over the two
XML streams. However, this perspective is a convenience only; XMPP
does not deal in documents but in XML streams and XML stanzas.
5.2. Stream Security
For the purpose of stream security, both Transport Layer Security
(see Section 6) and the Simple Authentication and Security Layer (see
Section 7) are mandatory to implement.
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When negotiating XML streams in XMPP 1.0, TLS SHOULD be used as
defined under Section 6 and SASL MUST be used as defined under
Section 7. The initial stream and the response stream MUST be
secured separately, although security in both directions MAY be
established via mechanisms that provide mutual authentication.
The initiating entity SHOULD NOT attempt to send XML stanzas
(Section 9) over the stream before the stream has been authenticated.
However, if it does attempt to do so, the receiving entity MUST NOT
accept such stanzas and MUST return a <not-authorized/> stream error
and then terminate both the XML stream and the underlying TCP
connection. Note: This applies to XML stanzas only (i.e.,
<message/>, <presence/>, and <iq/> elements qualified by the default
namespace) and not to XML elements used for stream negotiation (e.g.,
elements used to complete TLS negotiation (Section 6) or SASL
negotiation (Section 7)).
5.3. Stream Attributes
The attributes of the root <stream/> element are as follows.
5.3.1. from
In client-to-server communication, the 'from' attribute SHOULD be
included in the XML stream header sent from the initiating entity to
the receiving entity and (if included) MUST be set to the account
name (i.e., bare JID = <node@domain>) of the entity controlling the
client.
C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
In server-to-server communication, the 'from' attribute SHOULD be
included in the XML stream header sent from the initiating entity to
the receiving entity and (if included) MUST be set to a hostname
serviced by the initiating entity.
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P: <?xml version='1.0'?>
<stream:stream
from='example.net'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'>
In both client-to-server and server-to-server communications, the
'from' attribute MUST be included in the XML stream header by which
the receiving entity responds to the initiating entity and MUST be
set to a hostname serviced by the receiving entity that is granting
access to the initiating entity.
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
Note: Each entity MUST verify the identity of the other entity before
exchanging XML stanzas with it (see Section 15.3 and Section 15.4).
5.3.2. to
In both client-to-server and server-to-server communications, the
'to' attribute SHOULD be included in the XML stream header sent from
the initiating entity to the receiving entity and (if included) MUST
be set to a hostname serviced by the receiving entity.
C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
In client-to-server communication, if the client included a 'from'
address in the initial stream header then the server SHOULD include a
'to' attribute in the XML stream header by which it replies to the
client and (if included) MUST set the 'to' attribute to the bare JID
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specified in the 'from' attribute of the XML stream header sent from
the initiating entity to the receiving entity.
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
In server-to-server communication, if the initiating entity included
a 'from' address in the initial stream header then the receiving
entity SHOULD include a 'to' attribute in the XML stream header by
which it replies to the initiating entity and (if included) MUST set
the 'to' attribute to the hostname specified in the 'from' attribute
of the XML stream header sent from the initiating entity to the
receiving entity.
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='g4qSvGvBxJ+xeAd7QKezOQJFFlw='
to='example.net'
version='1.0'
xml:lang='en'
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'>
Note: Each entity MUST verify the identity of the other entity before
exchanging XML stanzas with it (see Section 15.3 and Section 15.4).
5.3.3. id
There SHOULD NOT be an 'id' attribute on the XML stream header sent
from the initiating entity to the receiving entity; however, if an
'id' attribute is included, it SHOULD be silently ignored by the
receiving entity.
C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
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xmlns:stream='http://etherx.jabber.org/streams'>
The 'id' attribute SHOULD be used only in the XML stream header from
the receiving entity to the initiating entity. This attribute is a
unique identifier created by the receiving entity to function as a
identifier for the initiating entity's two streams with the receiving
entity, and MUST be unique within the receiving application (normally
a server).
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
Note: The stream ID may be security-critical and therefore MUST be
both unpredictable and nonrepeating (see [RANDOM] for recommendations
regarding randomness for security purposes).
5.3.4. xml:lang
An 'xml:lang' attribute (as defined in Section 2.12 of [XML]) SHOULD
be included by the initiating entity on the header for the initial
stream to specify the default language of any human-readable XML
character data it sends over that stream.
C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
If the attribute is included, the receiving entity SHOULD remember
that value as the default for both the initial stream and the
response stream; if the attribute is not included, the receiving
entity SHOULD use a configurable default value for both streams,
which it MUST communicate in the header for the response stream.
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S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
For all stanzas sent over the initial stream, if the initiating
entity does not include an 'xml:lang' attribute, the receiving entity
SHOULD apply the default value; if the initiating entity does include
an 'xml:lang' attribute, the receiving entity MUST NOT modify or
delete it (see also Section 9.1.5). The value of the 'xml:lang'
attribute MUST conform to the NMTOKEN datatype (as defined in Section
2.3 of [XML]) and MUST conform to the format defined in [LANGTAGS].
5.3.5. version
The presence of the version attribute set to a value of at least
"1.0" signals support for the stream-related protocols (including
stream features) defined in this specification.
The version of XMPP specified herein is "1.0"; in particular, this
encapsulates the stream-related protocols (TLS negotiation
(Section 6), SASL negotiation (Section 7), and stream errors
(Section 5.8)), as well as the semantics of the three defined XML
stanza types (<message/>, <presence/>, and <iq/>).
The numbering scheme for XMPP versions is "<major>.<minor>". The
major and minor numbers MUST be treated as separate integers and each
number MAY be incremented higher than a single digit. Thus, "XMPP
2.4" would be a lower version than "XMPP 2.13", which in turn would
be lower than "XMPP 12.3". Leading zeros (e.g., "XMPP 6.01") MUST be
ignored by recipients and MUST NOT be sent.
The major version number should be incremented only if the stream and
stanza formats or required actions have changed so dramatically that
an older version entity would not be able to interoperate with a
newer version entity if it simply ignored the elements and attributes
it did not understand and took the actions specified in the older
specification.
The minor version number should be incremented only if significant
new capabilities have been added to the core protocol (e.g., a newly
defined value of the 'type' attribute for message, presence, or IQ
stanzas). The minor version number MUST be ignored by an entity with
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a smaller minor version number, but used for informational purposes
by the entity with the larger minor version number (e.g., the entity
with the larger minor version number would simply note that its
correspondent would not be able to understand that value of the
'type' attribute and therefore would not send it).
The following rules apply to the generation and handling of the
'version' attribute within stream headers:
1. The initiating entity MUST set the value of the 'version'
attribute on the initial stream header to the highest version
number it supports (e.g., if the highest version number it
supports is that defined in this specification, it MUST set the
value to "1.0").
2. The receiving entity MUST set the value of the 'version'
attribute on the response stream header to either the value
supplied by the initiating entity or the highest version number
supported by the receiving entity, whichever is lower. The
receiving entity MUST perform a numeric comparison on the major
and minor version numbers, not a string match on
"<major>.<minor>".
3. If the version number included in the response stream header is
at least one major version lower than the version number included
in the initial stream header and newer version entities cannot
interoperate with older version entities as described, the
initiating entity SHOULD generate an <unsupported-version/>
stream error and terminate the XML stream and underlying TCP
connection.
4. If either entity receives a stream header with no 'version'
attribute, the entity MUST consider the version supported by the
other entity to be "0.9" and SHOULD NOT include a 'version'
attribute in the stream header it sends in reply.
5.3.6. Summary
We can summarize the attributes of the root <stream/> element as
follows.
+----------+--------------------------+-------------------------+
| | initiating to receiving | receiving to initiating |
+----------+--------------------------+-------------------------+
| to | JID of receiver | JID of initiator |
| from | JID of initiator | JID of receiver |
| id | silently ignored | stream identifier |
| xml:lang | default language | default language |
| version | XMPP 1.0 supported | XMPP 1.0 supported |
+----------+--------------------------+-------------------------+
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Note: The attributes of the root <stream/> element are not prepended
by a 'stream:' prefix because, in accordance with Section 5.3 of
[XML-NAMES], the default namespace does not apply to attribute names.
5.4. Namespace Declarations
The stream element MUST possess both a streams namespace declaration
and a default namespace declaration (as "namespace declaration" is
defined in [XML-NAMES]). For detailed information regarding the
streams namespace and default namespace, see Section 12.2.
5.5. Stream Features
If the initiating entity includes the 'version' attribute set to a
value of at least "1.0" in the initial stream header, after sending
the header for the response stream the receiving entity MUST send a
<features/> child element (prefixed by the streams namespace prefix)
to the initiating entity in order to announce any stream-level
features that can be negotiated (or capabilities that otherwise need
to be advertised).
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <stream:features>
<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'>
<required/>
</starttls>
</stream:features>
Stream features are used mainly to advertise TLS negotiation
(Section 6), SASL negotiation (Section 7), and resource binding
(Section 8); however, stream features also can be used to advertise
features associated with various XMPP extensions. If an entity does
not understand or support a feature, it SHOULD silently ignore that
feature.
If one or more security features (e.g., TLS and SASL) need to be
successfully negotiated before a non-security-related feature (e.g.,
resource binding) can be offered, the non-security-related feature
SHOULD NOT be included in the stream features that are advertised
before the relevant security features have been negotiated.
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If a feature must be negotiated before the initiating entity may
proceed, that feature SHOULD include a <required/> child element.
If there are no features to be advertised (e.g., in the stream reset
initiated after successful SASL negotiation for a server-to-server
connection, or after resource binding for a client-to-server stream)
then the receiving entity MUST include an empty <stream:features/>
element after sending a stream header to the initiating entity.
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <stream:features/>
5.6. Closing Streams
At any time after XML streams have been negotiated between two
entities, either entity MAY close its stream to the other entity
(even in the absence of a stream error) by sending a closing stream
tag:
C: </stream:stream>
The entity that sends the closing stream tag SHOULD wait for the
other entity to also close its stream:
S: </stream:stream>
However, the entity that sends the first closing stream tag MAY
consider both streams to be void if the other entity does not send
its closing stream tag within a reasonable amount of time (where the
definition of "reasonable" is left up to the implementation or
deployment).
After an entity sends a closing stream tag, it MUST NOT send further
data over that stream.
After the entity that sent the first closing stream tag receives a
reciprocal closing stream tag from the other entity, it MUST
terminate the underlying TCP connection.
Note: There is one TCP connection for client-to-server streams, but
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there are two TCP connections for server-to-server streams.
5.7. Reconnection
It can happen that an XMPP server goes offline while servicing
connections from clients and from other servers. Because the number
of such connections can be quite large, the reconnection algorithm
employed by entities that seek to reconnect can have a significant
impact on software and network performance. The following guidelines
are RECOMMENDED:
o The time to live (TTL) specified in Domain Name System records
SHOULD be honored, even if DNS results are cached; if the TTL has
not expired, an entity that seeks to reconnect SHOULD NOT re-
resolve the server hostname before reconnecting.
o The time that expires before an entity first seeks to reconnect
SHOULD be randomized (e.g., so that all clients do not attempt to
reconnect 30 seconds after being disconnected).
o If the first reconnection attempt does not succeed, an entity
SHOULD back off exponentially on the time between subsequent
reconnection attempts.
5.8. Stream Errors
The root stream element MAY contain an <error/> child element that is
prefixed by the streams namespace prefix. The error child shall be
sent by a compliant entity (typically a server rather than a client)
if it perceives that a stream-level error has occurred.
5.8.1. Rules
The following rules apply to stream-level errors.
5.8.1.1. Stream Errors Are Unrecoverable
Stream-level errors are unrecoverable. Therefore, if an error occurs
at the level of the stream, the entity that detects the error MUST
send a stream error to the other entity, send a closing </stream>
tag, and terminate the underlying TCP connection.
C: <message><body></message>
S: <stream:error>
<xml-not-well-formed
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
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5.8.1.2. Stream Errors Can Occur During Setup
If the error occurs while the stream is being set up, the receiving
entity MUST still send the opening <stream> tag, include the <error/>
element as a child of the stream element, send the closing </stream>
tag, and terminate the underlying TCP connection.
C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://wrong.ns.example.org/'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
<stream:error>
<invalid-namespace
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.1.3. Stream Errors When the Host is Unspecified
If the initiating entity provides no 'to' attribute or provides an
unknown host in the 'to' attribute and the error occurs during stream
setup, the receiving entity SHOULD provide its authoritative hostname
in the 'from' attribute of the stream header sent before termination.
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C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://wrong.ns.example.org/'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
<stream:error>
<invalid-namespace
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.2. Syntax
The syntax for stream errors is as follows, where "defined-condition"
is a placeholder for one of the conditions defined under
Section 5.8.3.
<stream:error>
<defined-condition xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
[<text xmlns='urn:ietf:params:xml:ns:xmpp-streams'
xml:lang='langcode'>
descriptive text
</text>]
[application-specific condition element]
</stream:error>
The <error/> element:
o MUST contain a child element corresponding to one of the defined
stream error conditions (Section 5.8.3); this element MUST be
qualified by the 'urn:ietf:params:xml:ns:xmpp-streams' namespace.
o MAY contain a <text/> child element containing XML character data
that describes the error in more detail; this element MUST be
qualified by the 'urn:ietf:params:xml:ns:xmpp-streams' namespace
and SHOULD possess an 'xml:lang' attribute specifying the natural
language of the XML character data.
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o MAY contain a child element for an application-specific error
condition; this element MUST be qualified by an application-
defined namespace, and its structure is defined by that namespace
(see Section 5.8.4).
The <text/> element is OPTIONAL. If included, it SHOULD be used only
to provide descriptive or diagnostic information that supplements the
meaning of a defined condition or application-specific condition. It
SHOULD NOT be interpreted programmatically by an application. It
SHOULD NOT be used as the error message presented to a human user,
but MAY be shown in addition to the error message associated with the
included condition element (or elements).
5.8.3. Defined Stream Error Conditions
The following stream-level error conditions are defined.
5.8.3.1. bad-format
The entity has sent XML that cannot be processed.
C: <message><body></message>
S: <stream:error>
<bad-format
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
This error MAY be used instead of the more specific XML-related
errors, such as <bad-namespace-prefix/>, <invalid-xml/>, <restricted-
xml/>, <unsupported-encoding/>, and <xml-not-well-formed/>. However,
the more specific errors are preferred.
5.8.3.2. bad-namespace-prefix
The entity has sent a namespace prefix that is unsupported, or has
sent no namespace prefix on an element that requires such a prefix
(see Section 12.2).
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C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xmlns='jabber:client'
xmlns:foobar='http://etherx.jabber.org/streams'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
<stream:error>
<bad-namespace-prefix
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.3. conflict
The server is either (1) closing the existing stream for this entity
because a new stream has been initiated that conflicts with the
existing stream (2) is refusing a new stream for this entity because
allowing the new stream would conflict with an existing stream (e.g.,
because the server allows only a certain number of connections for
the same IP address).
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C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
<stream:error>
<conflict
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.4. connection-timeout
The entity has not generated any traffic over the stream for some
period of time (configurable according to a local service policy) and
therefore the connection is being dropped.
S: <stream:error>
<connection-timeout
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.5. host-gone
The value of the 'to' attribute provided by the initiating entity in
the stream header corresponds to a hostname that is no longer hosted
by the server.
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P: <?xml version='1.0'?>
<stream:stream
from='example.net'
to='foo.example.org'
version='1.0'
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='g4qSvGvBxJ+xeAd7QKezOQJFFlw='
to='example.net'
version='1.0'
xml:lang='en'
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'>
<stream:error>
<host-gone
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.6. host-unknown
The value of the 'to' attribute provided by the initiating entity in
the stream header does not correspond to a hostname that is hosted by
the server.
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P: <?xml version='1.0'?>
<stream:stream
from='example.net'
to='example.org'
version='1.0'
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='g4qSvGvBxJ+xeAd7QKezOQJFFlw='
to='example.net'
version='1.0'
xml:lang='en'
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'>
<stream:error>
<host-unknown
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.7. improper-addressing
A stanza sent between two servers lacks a 'to' or 'from' attribute
(or the attribute has no value).
P: <message from='juliet@example.com'>
<body>Wherefore art thou?</body>
</message>
S: <stream:error>
<improper-addressing
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.8. internal-server-error
The server has experienced a misconfiguration or an otherwise-
undefined internal error that prevents it from servicing the stream.
S: <stream:error>
<internal-server-error
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
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5.8.3.9. invalid-from
The JID or hostname provided in a 'from' address does not match an
authorized JID or validated domain negotiated between servers via
SASL, or between a client and a server via authentication and
resource binding.
P: <message from='romeo@example.org' to='juliet@example.com'>
<body>Neither, fair saint, if either thee dislike.</body>
</message>
S: <stream:error>
<improper-addressing
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.10. invalid-id
The stream ID or server dialback ID is invalid or does not match an
ID previously provided (the following example is from server
dialback; see [XEP-0220]).
P: <db:verify
from='example.net'
to='example.com'
id='unknown-id-here'
type='invalid'/>
S: <stream:error>
<invalid-id
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.11. invalid-namespace
The streams namespace name is something other than
"http://etherx.jabber.org/streams" (see Section 12.2).
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C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xmlns='jabber:client'
xmlns:stream='http://wrong.ns.example.org/'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
<stream:error>
<invalid-namespace
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.12. invalid-xml
The entity has sent invalid XML over the stream to a server that
performs validation (see Section 12.3). (In the following example, a
peer attempts to send an IQ stanza of type "subscribe" but there is
no such value for the 'type' attribute.)
P: <iq from='example.net'
id='some-id'
to='example.com'
type='subscribe'>
<ping xmlns='urn:xmpp:ping'/>
</iq>
S: <stream:error>
<invalid-xml
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.13. not-authorized
The entity has attempted to send XML stanzas before the stream has
been authenticated, or otherwise is not authorized to perform an
action related to stream negotiation; the receiving entity MUST NOT
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process the offending stanza before sending the stream error. (In
the following example, a client attempts to send XML stanzas before
authenticating with the server.)
C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
C: <message to='romeo@example.net'>
<body>Wherefore art thou?</body>
</message>
S: <stream:error>
<not-authorized
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.14. policy-violation
The entity has violated some local service policy (e.g., the stanza
exceeds a configured size limit); the server MAY choose to specify
the policy in the <text/> element or an application-specific
condition element.
C: <message to='juliet@example.com' id='foo'>
<body>[ ... the-emacs-manual ... ]</body>
</message>
S: <stream:error>
<policy-violation
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
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S: </stream:stream>
5.8.3.15. remote-connection-failed
The server is unable to properly connect to a remote entity that is
required for authentication or authorization.
C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
<stream:error>
<remote-connection-failed
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.16. resource-constraint
The server lacks the system resources necessary to service the
stream.
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C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
<stream:error>
<resource-constraint
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.17. restricted-xml
The entity has attempted to send restricted XML features such as a
comment, processing instruction, DTD, entity reference, or unescaped
character (see Section 12.1).
C: <message to='juliet@example.com'>
<body><!--just a comment!--></body>
</message>
S: <stream:error>
<restricted-xml
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.18. see-other-host
The server will not provide service to the initiating entity but is
redirecting traffic to another host; the XML character data of the
<see-other-host/> element returned by the server SHOULD specify the
alternate hostname or IP address at which to connect, which SHOULD be
a valid domain identifier but may also include a port number; if no
port is specified, the initiating entity SHOULD perform a [DNS-SRV]
lookup on the provided domain identifier but MAY assume that it can
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connect to that domain identifier at the standard XMPP ports (5222
for client-to-server connections and 5269 for server-to-server
connections).
C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
<stream:error>
<see-other-host
xmlns='urn:ietf:params:xml:ns:xmpp-streams'>
xmpp.example.com:9090
</see-other-host>
</stream:error>
</stream:stream>
5.8.3.19. system-shutdown
The server is being shut down and all active streams are being
closed.
S: <stream:error>
<system-shutdown
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.20. undefined-condition
The error condition is not one of those defined by the other
conditions in this list; this error condition SHOULD be used only in
conjunction with an application-specific condition.
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S: <stream:error>
<undefined-condition
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
<app-error xmlns='some-application-ns'/>
</stream:error>
</stream:stream>
5.8.3.21. unsupported-encoding
The initiating entity has encoded the stream in an encoding that is
not supported by the server (see Section 12.5).
C: <?xml version='1.0' encoding='UTF-16'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
<stream:error>
<unsupported-encoding
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.22. unsupported-stanza-type
The initiating entity has sent a first-level child of the stream that
is not supported by the server.
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C: <pubsub>
<publish node='princely_musings'>
<item id='ae890ac52d0df67ed7cfdf51b644e901'>
<entry xmlns='http://www.w3.org/2005/Atom'>
<title>Soliloquy</title>
<summary>
To be, or not to be: that is the question:
Whether 'tis nobler in the mind to suffer
The slings and arrows of outrageous fortune,
Or to take arms against a sea of troubles,
And by opposing end them?
</summary>
<link rel='alternate' type='text/html'
href='http://denmark.lit/2003/12/13/atom03'/>
<id>tag:denmark.lit,2003:entry-32397</id>
<published>2003-12-13T18:30:02Z</published>
<updated>2003-12-13T18:30:02Z</updated>
</entry>
</item>
</publish>
</pubsub>
S: <stream:error>
<unsupported-stanza-type
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.23. unsupported-version
The value of the 'version' attribute provided by the initiating
entity in the stream header specifies a version of XMPP that is not
supported by the server; the server MAY specify the version(s) it
supports in the <text/> element.
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C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='11.0'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
<stream:error>
<unsupported-version
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.3.24. xml-not-well-formed
<xml-not-well-formed/> -- the initiating entity has sent XML that is
not well-formed as defined by [XML].
C: <message><body></message>
S: <stream:error>
<xml-not-well-formed
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
5.8.4. Application-Specific Conditions
As noted, an application MAY provide application-specific stream
error information by including a properly-namespaced child in the
error element. The application-specific element SHOULD supplement or
further qualify a defined element. Thus the <error/> element will
contain two or three child elements:
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C: <message>
<body>
My keyboard layout is:
QWERTYUIOP{}|
ASDFGHJKL:"
ZXCVBNM<>?
</body>
</message>
S: <stream:error>
<xml-not-well-formed
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
<text xml:lang='en' xmlns='urn:ietf:params:xml:ns:xmpp-streams'>
Some special application diagnostic information!
</text>
<escape-your-data xmlns='application-ns'/>
</stream:error>
</stream:stream>
5.9. Simplified Stream Examples
This section contains two simplified examples of a stream-based
connection of a client on a server (where the "C" lines are sent from
the client to the server, and the "S" lines are sent from the server
to the client); these examples are included for the purpose of
illustrating the concepts introduced thus far.
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A basic connection:
C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
[ ... encryption, authentication, and resource binding ... ]
C: <message from='juliet@example.com/balcony'
to='romeo@example.net'
xml:lang='en'>
<body>Art thou not Romeo, and a Montague?</body>
</message>
S: <message from='romeo@example.net/orchard'
to='juliet@example.com/balcony'
xml:lang='en'>
<body>Neither, fair saint, if either thee dislike.</body>
</message>
C: </stream:stream>
S: </stream:stream>
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A connection gone bad:
C: <?xml version='1.0'?>
<stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <?xml version='1.0'?>
<stream:stream
from='example.com'
id='++TR84Sm6A3hnt3Q065SnAbbk3Y='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
[ ... encryption, authentication, and resource binding ... ]
C: <message from='juliet@example.com/balcony'
to='romeo@example.net'
xml:lang='en'>
<body>Bad XML, no closing body tag!
</message>
S: <stream:error>
<xml-not-well-formed
xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</stream:error>
</stream:stream>
More detailed examples are provided under Section 10.
6. STARTTLS Negotiation
6.1. Overview
XMPP includes a method for securing the stream from tampering and
eavesdropping. This channel encryption method makes use of the
Transport Layer Security protocol (see [TLS]), specifically a
"STARTTLS" extension that is modelled after similar extensions for
the [IMAP], [POP3], and [ACAP] protocols as described in [USINGTLS].
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The XML namespace name for the STARTTLS extension is
'urn:ietf:params:xml:ns:xmpp-tls'.
Support for STARTTLS is REQUIRED in XMPP client and server
implementations. An administrator of a given deployment may require
the use of TLS for client-to-server communication, server-to-server
communication, or both. A deployed client should use TLS to secure
its stream with a server prior to attempting the completion of SASL
negotiation (Section 7), and deployed servers should use TLS between
two domains for the purpose of securing server-to-server
communication.
6.2. Rules
6.2.1. Data Formatting
The entities MUST NOT send any white space characters (matching
production [3] content of [XML]) within the root stream element as
separators between elements (any white space characters shown in the
STARTTLS examples provided in this document are included for the sake
of readability only); this prohibition helps to ensure proper
security layer byte precision.
6.2.2. Order of Negotiation
If the initiating entity chooses to use TLS, STARTTLS negotiation
MUST be completed before proceeding to SASL negotiation (Section 7);
this order of negotiation is required to help safeguard
authentication information sent during SASL negotiation, as well as
to make it possible to base the use of the SASL EXTERNAL mechanism on
a certificate (or other credentials) provided during prior TLS
negotiation.
6.3. Process
6.3.1. Exchange of Stream Headers and Stream Features
The initiating entity resolves the hostname of the receiving entity
as specified under Section 4, opens a TCP connection to the
advertised port at the resolved IP address, and sends an initial
stream header to the receiving entity; if the initiating entity is
capable of STARTTLS negotiation, it MUST include the 'version'
attribute set to a value of at least "1.0" in the initial stream
header.
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I: <stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
The receiving entity MUST send a response stream header to the
initiating entity over the TCP connection opened by the initiating
entity (for client-to-server streams) or over a new TCP connection
(for server-to-server streams); if the receiving entity is capable of
STARTTLS negotiation, it MUST include the 'version' attribute set to
a value of at least "1.0" in the response stream header.
R: <stream:stream
from='example.com'
id='t7AMCin9zjMNwQKDnplntZPIDEI='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
The receiving entity then MUST send stream features to the initiating
entity, which SHOULD include a <starttls/> element (qualified by the
'urn:ietf:params:xml:ns:xmpp-tls' namespace) to indicate that the
receiving entity supports STARTTLS negotiation.
R: <stream:features>
<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
</stream:features>
If the receiving entity requires the use of STARTTLS, it SHOULD
include an empty <required/> element as a child of the <starttls/>
element.
R: <stream:features>
<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'>
<required/>
</starttls>
</stream:features>
6.3.2. Initiation of STARTTLS Negotiation
In order to begin the STARTTLS negotiation, the initiating entity
issues the STARTTLS command (i.e., a <starttls/> element qualified by
the 'urn:ietf:params:xml:ns:xmpp-tls' namespace) to instruct the
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receiving entity that it wishes to begin a STARTTLS negotiation to
secure the stream.
I: <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
The receiving entity MUST reply with either a <proceed/> element
(proceed case) or a <failure/> element (failure case) qualified by
the 'urn:ietf:params:xml:ns:xmpp-tls' namespace.
If the failure case occurs, the receiving entity MUST return a
<failure/> element qualified by the 'urn:ietf:params:xml:ns:xmpp-tls'
namespace, terminate the XML stream, and terminate the underlying TCP
connection. Causes for the failure case include but are not limited
to:
1. The initiating entity has sent a malformed STARTTLS command.
2. The receiving entity does not offer STARTTLS negotiation either
temporarily or permanently.
3. The receiving entity cannot complete STARTTLS negotiation because
of an internal error.
R: <failure xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
R: </stream:stream>
If the proceed case occurs, the receiving entity MUST return a
<proceed/> element qualified by the 'urn:ietf:params:xml:ns:xmpp-tls'
namespace.
R: <proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
Note: The receiving entity MUST consider the TLS negotiation to have
begun immediately after sending the closing '>' character of the
<proceed/> element to the initiating entity. The initiating entity
MUST consider the TLS negotiation to have begun immediately after
receiving the closing '>' character of the <proceed/> element from
the receiving entity.
6.3.3. TLS Negotiation
The entities MUST now attempt to complete TLS negotiation over the
TCP connection by following the process defined in [TLS].
Note: The entities MUST NOT send any further XML data until the TLS
negotiation has either failed or succeeded.
If the receiving entity presents a certificate during TLS
negotiation, the initiating entity MUST validate the certificate in
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order to determine if the TLS negotiation shall succeed (see
Section 15.2 regarding certificate validation procedures).
Specifically, the certificate MUST be checked against the hostname as
provided by the initiating entity (e.g., a user), not the hostname as
resolved via the Domain Name System; e.g., if the user specifies a
hostname of "example.net" but a [DNS-SRV] lookup returns
"xmpp.example.net", the certificate MUST be checked as "example.net".
See Section 6.4 for information about the representation of XMPP
addresses in certificates.
Note: See Section 15.7 regarding ciphers that MUST be supported for
TLS; naturally, other ciphers MAY be supported as well.
6.3.4. Failure
If the TLS negotiation results in failure, the receiving entity MUST
terminate the TCP connection.
Note: It is not necessary to send a closing </stream> tag before
terminating the TCP connection, since the receiving entity and
initiating entity MUST consider the original stream to be closed upon
failure of the TLS negotiation.
6.3.5. Success
If the TLS negotiation is successful, then the entities MUST proceed
as follows.
The receiving entity MUST discard any knowledge obtained in an
insecure manner from the initiating entity before TLS took effect.
The initiating entity MUST discard any knowledge obtained in an
insecure manner from the receiving entity before TLS took effect.
The initiating entity MUST send a new stream header to the receiving
entity over the secured TCP connection.
I: <stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
Note: It is not necessary to send a closing </stream> tag before
sending the initial stream header, since the receiving entity and
initiating entity MUST consider the original stream to be closed upon
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success of the TLS negotiation.
The receiving entity MUST respond with a response stream header.
R: <stream:stream
from='example.com'
id='vgKi/bkYME8OAj4rlXMkpucAqe4='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
The receiving entity also MUST send stream features to the initiating
entity, which MUST NOT include the STARTTLS feature but which SHOULD
include the SASL stream feature as described under Section 7.
R: <stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>EXTERNAL</mechanism>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
<required/>
</mechanisms>
</stream:features>
6.4. Representation of JIDs in Certificates
TLS negotiation is commonly based on a digital certificate presented
by the receiving entity (or in the case of mutual authentication both
the receiving entity and the initiating entity).
If a JID for an XMPP user account is represented in a certificate, it
MUST be represented as a UTF8String within an otherName entity inside
the subjectAltName, using the [ASN.1] Object Identifier "id-on-
xmppAddr" specified in this section.
If a JID for an XMPP server is represented in a certificate, it
SHOULD be represented as a UTF8String within an otherName entity
inside the subjectAltName, using the [ASN.1] Object Identifier "id-
on-xmppAddr" specified in this section. However, in addition to or
instead of the "id-on-xmppAddr" representation, it MAY be represented
as a subjectAltName extension of type dNSName; this dNSName MAY
contain the wildcard character '*', which applies only to the left-
most domain name component or component fragment and is considered to
match any single component or component fragment (e.g., *.example.com
matches foo.example.com but not bar.foo.example.com, and
im*.example.net matches im1.example.net and im2.example.net but not
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chat.example.net).
The [ASN.1] Object Identifier "id-on-xmppAddr" is defined as follows.
id-pkix OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7) }
id-on OBJECT IDENTIFIER ::= { id-pkix 8 } -- other name forms
id-on-xmppAddr OBJECT IDENTIFIER ::= { id-on 5 }
XmppAddr ::= UTF8String
This Object Identifier MAY be represented in dotted display format
(i.e., "1.3.6.1.5.5.7.8.5") or in the Uniform Resource Name notation
specified in [URN-OID] (i.e., "urn:oid:1.3.6.1.5.5.7.8.5").
Thus for example the JID "juliet@example.com" as included in a
certificate could be formatted in any of the following three ways:
o subjectAltName=otherName:id-on-xmppAddr;UTF8:juliet@example.com
o subjectAltName=otherName:1.3.6.1.5.5.7.8.5;UTF8:juliet@example.com
o subjectAltName=otherName:urn:oid:1.3.6.1.5.5.7.8.5;UTF8:juliet@
example.com
7. SASL Negotiation
7.1. Overview
XMPP includes a method for authenticating a stream by means of an
XMPP-specific profile of the Simple Authentication and Security Layer
protocol (see [SASL]). SASL provides a generalized method for adding
authentication support to connection-based protocols, and XMPP uses
an XML namespace profile of SASL that conforms to the profiling
requirements of [SASL].
Support for SASL is REQUIRED in XMPP client and server
implementations.
7.2. Rules
7.2.1. Data Formatting
The following formatting rules apply to the data sent during SASL
negotiation:
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1. The entities MUST NOT send any white space characters (matching
production [3] content of [XML]) within the root stream element
as separators between elements (any white space characters shown
in the SASL examples provided in this document are included for
the sake of readability only); this prohibition helps to ensure
proper security layer byte precision.
2. Any XML character data contained within the XML elements MUST be
encoded using base64, where the encoding adheres to the
definition in Section 4 of [BASE64] and where the padding bits
are set to zero.
7.2.2. Security Layers
Upon successful SASL negotiation that involves negotiation of a
security layer, the initiating entity MUST discard any knowledge
obtained from the receiving entity which was not obtained from the
SASL negotiation itself.
Upon successful SASL negotiation that involves negotiation of a
security layer, the receiving entity MUST discard any knowledge
obtained from the initiating entity which was not obtained from the
SASL negotiation itself. The receiving entity SHOULD also include an
updated list of SASL mechanisms with the stream features so that the
initiating entity is able to detect any changes to the list of
mechanisms supported by the receiving entity.
7.2.3. Simple Usernames
If provision of a "simple username" is supported by the selected SASL
mechanism (e.g., this is supported by the DIGEST-MD5 and CRAM-MD5
mechanisms but not by the EXTERNAL and GSSAPI mechanisms), during
authentication the initiating entity SHOULD provide as the simple
username its sending domain (IP address or fully qualified domain
name as contained in an XMPP domain identifier) in the case of
server-to-server communication or its registered account name (user
or node name as contained in an XMPP node identifier) in the case of
client-to-server communication. In either case, the initiating
entity MUST ensure that the username adheres to the [NAMEPREP] or
Nodeprep (Appendix A) profile of [STRINGPREP] (as appropriate) before
sending it to the receiving entity.
7.2.4. Authorization Identities
If the initiating entity wishes to act on behalf of another entity
and the selected SASL mechanism supports transmission of an
authorization identity, the initiating entity MUST provide an
authorization identity during SASL negotiation. If the initiating
entity does not wish to act on behalf of another entity, it MUST NOT
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provide an authorization identity. As specified in [SASL], the
initiating entity MUST NOT provide an authorization identity unless
the authorization identity is different from the default
authorization identity derived from the authentication identity. If
provided, the value of the authorization identity MUST be of the form
<domain> (i.e., an XMPP domain identifier only) for servers and of
the form <node@domain> (i.e., node identifier and domain identifier)
for clients.
7.3. Process
The process for SASL negotiation is as follows.
7.3.1. Exchange of Stream Headers and Stream Features
If SASL negotiation follows successful STARTTLS negotation
(Section 6), then the SASL negotiation occurs over the existing
stream. If not, the initiating entity resolves the hostname of the
receiving entity as specified under Section 4, opens a TCP connection
to the advertised port at the resolved IP address, and sends an
initial stream header to the receiving entity; if the initiating
entity is capable of STARTTLS negotiation, it MUST include the
'version' attribute set to a value of at least "1.0" in the initial
stream header.
I: <stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
The receiving entity MUST send a response stream header to the
initiating entity; if the receiving entity is capable of SASL
negotiation, it MUST include the 'version' attribute set to a value
of at least "1.0" in the response stream header.
R: <stream:stream
from='example.com'
id='vgKi/bkYME8OAj4rlXMkpucAqe4='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
The receiving entity also MUST send stream features to the initiating
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entity, which SHOULD include the SASL stream feature, i.e., a
<mechanisms/> element (qualified by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace) that contains one
<mechanism/> child element for each authentication mechanism the
receiving entity offers to the initiating entity. The order of
<mechanism/> elements in the XML indicates the preference order of
the SASL mechanisms according to the receiving entity.
R: <stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>EXTERNAL</mechanism>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
</mechanisms>
</stream:features>
Note: If the initiating entity presents a valid certificate during
prior TLS negotiation, the receiving entity SHOULD offer the SASL
EXTERNAL mechanism to the initiating entity during SASL negotiation
(refer to [SASL]), although the EXTERNAL mechanism MAY be offered
under other circumstances as well.
Note: If TLS negotiation (Section 6) needs to be completed before a
particular authentication mechanism may be used, the receiving entity
MUST NOT provide that mechanism in the list of available SASL
authentication mechanisms prior to TLS negotiation.
Note: See Section 15.7 regarding mechanisms that MUST be supported;
naturally, other SASL mechanisms MAY be supported as well (best
practices for the use of several SASL mechanisms in the context of
XMPP are described in [XEP-0175] and [XEP-0178]).
If successful SASL negotiation is required for interaction with the
receiving entity, it SHOULD signal that fact by including a
<required/> element as a child of the <mechanisms/> element.
R: <stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>EXTERNAL</mechanism>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
<required/>
</mechanisms>
</stream:features>
Note: The receiving entity MAY include an application-specific child
element inside the <mechanisms/> element in order to provide
information that may be needed by the initiating in order to complete
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successful SASL negotiation using one or more of the offered
mechanisms; however, the syntax and semantics of any such element are
out of scope for this specification.
7.3.2. Initiation
In order to begin the SASL negotiation, the initiating entity sends
an <auth/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace and includes an
appropriate value for the 'mechanism' attribute. This element MAY
contain XML character data (in SASL terminology, the "initial
response") if the mechanism supports or requires it; if the
initiating entity needs to send a zero-length initial response, it
MUST transmit the response as a single equals sign ("="), which
indicates that the response is present but contains no data.
I: <auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
mechanism='DIGEST-MD5'>=</auth>
7.3.3. Challenge-Response Sequence
If necessary, the receiving entity challenges the initiating entity
by sending a <challenge/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace; this element MAY
contain XML character data (which MUST be generated in accordance
with the definition of the SASL mechanism chosen by the initiating
entity).
R: <challenge xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
cmVhbG09ImV4YW1wbGUuY29tIixub25jZT0iT0E2TUc5dEVRR20yaGgiLHFvcD0i
YXV0aCIsY2hhcnNldD11dGYtOCxhbGdvcml0aG09bWQ1LXNlc3MK
</challenge>
The decoded challenge is:
realm="example.com",nonce="OA6MG9tEQGm2hh",
qop="auth",charset=utf-8,algorithm=md5-sess
Note: If the receiving entity does not specify a 'realm' value, the
initiating entity MUST default it to the domain identifier portion of
the receiving entity's JID.
The initiating entity responds to the challenge by sending a
<response/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace; this element MAY
contain XML character data (which MUST be generated in accordance
with the definition of the SASL mechanism chosen by the initiating
entity).
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I: <response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
dXNlcm5hbWU9Imp1bGlldCIscmVhbG09ImV4YW1wbGUuY29tIixub25jZT0iT0E2
TUc5dEVRR20yaGgiLGNub25jZT0iT0E2TUhYaDZWcVRyUmsiLG5jPTAwMDAwMDAx
LHFvcD1hdXRoLGRpZ2VzdC11cmk9InhtcHAvZXhhbXBsZS5jb20iLHJlc3BvbnNl
PWQzODhkYWQ5MGQ0YmJkNzYwYTE1MjMyMWYyMTQzYWY3LGNoYXJzZXQ9dXRmLTgK
</response>
The decoded response is:
username="juliet",realm="example.com",
nonce="OA6MG9tEQGm2hh",cnonce="OA6MHXh6VqTrRk",
nc=00000001,qop=auth,digest-uri="xmpp/example.com",
response=d388dad90d4bbd760a152321f2143af7,charset=utf-8
If necessary, the receiving entity sends more challenges and the
initiating entity sends more responses.
This series of challenge/response pairs continues until one of three
things happens:
o The initiating entity aborts the handshake.
o The receiving entity reports failure of the handshake.
o The receiving entity reports success of the handshake.
These scenarios are described in the following sections.
7.3.4. Abort
The initiating entity aborts the handshake by sending an <abort/>
element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl'
namespace.
I: <abort xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
Upon receiving an <abort/> element, the receiving entity MUST return
an <aborted/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace.
R: <aborted xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
The receiving entity SHOULD allow a configurable but reasonable
number of retries (at least 2 and no more than 5); this enables the
initiating entity (e.g., an end-user client) to tolerate incorrectly-
provided credentials (e.g., a mistyped password) without being forced
to reconnect.
If the initiating entity exceeds the number of retries, the receiving
entity MUST terminate the TCP connection.
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7.3.5. Failure
The receiving entity reports failure of the handshake by sending a
<failure/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace (the particular cause of
failure SHOULD be communicated in an appropriate child element of the
<failure/> element as defined under Section 7.5).
R: <failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<not-authorized/>
</failure>
If the failure case occurs, the receiving entity SHOULD allow a
configurable but reasonable number of retries (at least 2 and no more
than 5); this enables the initiating entity (e.g., an end-user
client) to tolerate incorrectly-provided credentials (e.g., a
mistyped password) without being forced to reconnect.
If the initiating entity exceeds the number of retries, the receiving
entity MUST terminate the TCP connection.
7.3.6. Success
The receiving entity reports success of the handshake by sending a
<success/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace; this element MAY
contain XML character data (in SASL terminology, "additional data
with success") if required by the chosen SASL mechanism; if the
receiving entity needs to send additional data of zero length, it
MUST transmit the data as a single equals sign ("=").
R: <success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZAo=
</success>
The decoded value for subsequent authentication is:
rspauth=ea40f60335c427b5527b84dbabcdfffd
Upon receiving the <success/> element, the initiating entity MUST
initiate a new stream over the existing TCP connection by sending an
initial stream header to the receiving entity.
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I: <stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
Note: It is not necessary to send a closing </stream> tag before
sending the initial stream header, since the receiving entity and
initiating entity MUST consider the original stream to be closed upon
sending or receiving the <success/> element.
Upon receiving the initial stream header from the initiating entity,
the receiving entity MUST respond by sending a new XML stream header
to the initiating entity.
R: <stream:stream
from='example.com'
id='gPybzaOzBmaADgxKXu9UClbprp0='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
The receiving entity MUST also send stream features, containing any
further available features or containing no features (via an empty
<features/> element); any such additional features not defined herein
MUST be defined by the relevant extension to XMPP.
R: <stream:features>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<required/>
</bind>
</stream:features>
7.4. SASL Definition
The profiling requirements of [SASL] require that the following
information be supplied by a protocol definition:
service name: "xmpp"
initiation sequence: After the initiating entity provides an opening
XML stream header and the receiving entity replies in kind, the
receiving entity provides a list of acceptable authentication
methods. The initiating entity chooses one method from the list
and sends it to the receiving entity as the value of the
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'mechanism' attribute possessed by an <auth/> element, optionally
including an initial response to avoid a round trip.
exchange sequence: Challenges and responses are carried through the
exchange of <challenge/> elements from receiving entity to
initiating entity and <response/> elements from initiating entity
to receiving entity. The receiving entity reports failure by
sending a <failure/> element and success by sending a <success/>
element; the initiating entity aborts the exchange by sending an
<abort/> element. Upon successful negotiation, both sides
consider the original XML stream to be closed and new stream
headers are sent by both entities.
security layer negotiation: The security layer takes effect
immediately after sending the closing '>' character of the
<success/> element for the receiving entity, and immediately after
receiving the closing '>' character of the <success/> element for
the initiating entity. The order of layers is first [TCP], then
[TLS], then [SASL], then XMPP.
use of the authorization identity: The authorization identity may be
used by XMPP to denote the non-default <node@domain> of a client
or the sending <domain> of a server; an empty string is equivalent
to an absent authorization identity.
7.5. SASL Errors
The following SASL-related error conditions are defined.
7.5.1. aborted
The receiving entity acknowledges an <abort/> element sent by the
initiating entity; sent in reply to the <abort/> element.
I: <abort xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
R: <failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<aborted/>
</failure>
7.5.2. incorrect-encoding
The data provided by the initiating entity could not be processed
because the [BASE64] encoding is incorrect (e.g., because the
encoding does not adhere to the definition in Section 4 of [BASE64]);
sent in reply to a <response/> element or an <auth/> element with
initial response data.
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I: <auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
mechanism='DIGEST-MD5'>[ ... ]</auth>
R: <failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<incorrect-encoding/>
</failure>
7.5.3. invalid-authzid
The authzid provided by the initiating entity is invalid, either
because it is incorrectly formatted or because the initiating entity
does not have permissions to authorize that ID; sent in reply to a
<response/> element or an <auth/> element with initial response data.
I: <response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
[ ... ]
</response>
R: <failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<invalid-authzid/>
</failure>
7.5.4. invalid-mechanism
The initiating entity did not provide a mechanism or requested a
mechanism that is not supported by the receiving entity; sent in
reply to an <auth/> element.
I: <auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
mechanism='CRAM-MD5'/>
R: <failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<invalid-mechanism/>
</failure>
7.5.5. malformed-request
The request is malformed (e.g., the <auth/> element includes an
initial response but the mechanism does not allow that); sent in
reply to an <abort/>, <auth/>, <challenge/>, or <response/> element.
I: <auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
mechanism='ANONYMOUS'>[ ... ]</auth>
R: <failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<malformed-request/>
</failure>
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7.5.6. mechanism-too-weak
The mechanism requested by the initiating entity is weaker than
server policy permits for that initiating entity; sent in reply to an
<auth/> element (with or without initial response data) or a
<response/> element.
I: <auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
mechanism='PLAIN'/>
R: <failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism-too-weak/>
</failure>
7.5.7. not-authorized
The authentication failed because the initiating entity did not
provide proper credentials; sent in reply to a <response/> element or
an <auth/> element with initial response data.
I: <response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
[ ... ]
</response>
R: <failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<not-authorized/>
</failure>
Note: This error condition includes but is not limited to the case of
incorrect credentials or an unknown username. In order to discourage
directory harvest attacks, no differentiation is made between
incorrect credentials and an unknown username.
7.5.8. temporary-auth-failure
The authentication failed because of a temporary error condition
within the receiving entity, and the initiating entity should try
again later; sent in reply to an <auth/> element or <response/>
element.
I: <response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
[ ... ]
</response>
R: <failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<temporary-auth-failure/>
</failure>
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8. Resource Binding
8.1. Overview
After a client authenticates with a server, it MUST bind a specific
resource to the stream so that the server can properly address the
client (see Section 3), i.e., there MUST be an XMPP resource
identifier associated with the bare JID (<node@domain>) of the client
with the result that the address for use over that stream is a full
JID of the form <node@domain/resource>. This ensures that the server
can deliver XML stanzas to and receive XML stanzas from the client
(see Section 11). After binding a resource to the stream, the client
is referred to as a connected resource.
If, before completing the resource binding step, the client attempts
to send an outbound XML stanza (i.e., a stanza not directed to the
server itself or to the client's own account), the server MUST NOT
process the stanza and SHOULD return a <not-authorized/> stream error
to the client.
Support for resource binding is REQUIRED in XMPP client and server
implementations.
8.2. Advertising Support
Upon receiving a success indication within the SASL negotiation, the
client MUST send a new stream header to the server, to which the
server MUST respond with a stream header as well as a list of
available stream features. Specifically, for client-to-server
streams the server MUST include a <bind/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-bind' namespace in the stream features
it presents to the client; this <bind/> element SHOULD include an
empty <required/> element to explicitly indicate that resource
binding must be completed at this stage of the stream negotiation
process. (Note: The server SHOULD NOT include the <bind/> stream
feature until after successful SASL negotiation.)
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S: <stream:stream
from='example.com'
id='gPybzaOzBmaADgxKXu9UClbprp0='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <stream:features>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<required/>
</bind>
</stream:features>
Upon being so informed that resource binding is required, the client
MUST bind a resource to the stream as described in the following
sections.
8.3. Server-Generated Resource Identifier
A server that supports resource binding MUST be able to generate an
XMPP resource identifier on behalf of a client. The resource
identifier generated by the server MUST at a minimum be unique among
the connected resources for that <node@domain> and SHOULD be random
since the resource identifier may be security-critical. It is
RECOMMENDED that the server-generated resource identifier be a
Universally Unique Identifier (UUID), for which the format specified
in [UUID] is RECOMMENDED.
It is RECOMMENDED for the client to ask its server to generate an
appropriate resource identifier on its behalf, rather than generating
a resource on its own and requesting that the server accept the
client-generated resource identifer.
8.3.1. Success Case
A client requests a server-generated resource identifier by sending
an IQ stanza of type "set" (see Section 9.2.3) containing an empty
<bind/> element qualified by the 'urn:ietf:params:xml:ns:xmpp-bind'
namespace.
C: <iq id='bind_1' type='set'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/>
</iq>
Once the server has generated an XMPP resource identifier for the
client, it MUST return an IQ stanza of type "result" to the client,
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which MUST include a <jid/> child element that specifies the full JID
for the connected resource as determined by the server.
S: <iq id='bind_1' type='result'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<jid>
juliet@example.com/4db06f06-1ea4-11dc-aca3-000bcd821bfb
</jid>
</bind>
</iq>
8.3.2. Error Case
It is possible that the client is not allowed to bind a resource to
the stream (e.g., because the node or user has reached a limit on the
number of connected resources allowed). In this case, the server
MUST return a <not-allowed/> stanza error to the client.
S: <iq id='bind_1' type='error'>
<error type='cancel'>
<not-allowed xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
8.4. Client-Generated Resource Identifier
A client MAY attempt to specify the resource identifier on its own
rather than asking the server to generate a resource identifier on
its behalf.
8.4.1. Success Case
A client asks its server to accept a client-generated resource
identifier by sending an IQ stanza of type "set" containing a <bind/>
element with a child <resource/> element containing non-zero-length
XML character data.
C: <iq id='bind_2' type='set'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<resource>balcony</resource>
</bind>
</iq>
The server MAY accept the resource identifier provided by the client,
in which case it returns an IQ stanza of type "result" to the client,
including a <jid/> child element that specifies the full JID for the
connected resource.
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S: <iq id='bind_2' type='result'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<jid>juliet@example.com/balcony</jid>
</bind>
</iq>
However, the server MAY instead override the client-generated
resource identifier and generate a resource identifier on behalf of
the client, as shown in the previous section.
8.4.2. Error Cases
When a client attempts to set its own XMPP resource identifier during
resource binding, the following stanza error conditions are possible:
o The client is not allowed to bind a resource to the stream (e.g.,
because the node or user has reached a limit on the number of
connected resources allowed).
o The provided resource identifier cannot be processed by the
server, e.g. because it is not in accordance with the Resourceprep
(Appendix B) profile of [STRINGPREP]).
o The provided resource identifier is already in use but the server
does not allow binding of multiple connected resources with the
same identifier.
8.4.2.1. Not Allowed
If the client is not allowed to bind a resource to the stream, the
server MUST return a <not-allowed/> error.
S: <iq id='bind_2' type='error'>
<error type='cancel'>
<not-allowed xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
8.4.2.2. Bad Request
If the provided resource identifier cannot be processed by the
server, the server SHOULD return a <bad-request/> error (but MAY
instead apply the Resourceprep (Appendix B) profile of [STRINGPREP]
or otherwise process the resource identifier so that it is in
conformance).
S: <iq id='bind_2' type='error'>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
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</iq>
8.4.2.3. Conflict
If there is already a connected resource of the same name, the server
MUST do one of the following:
1. Not accept the resource identifier provided by the client but
instead override it with an XMPP resource identifier that the
server generates.
2. Terminate the current resource and allow the newly-requested
resource.
3. Disallow the newly-requested resource and maintain the current
resource.
Which of these the server does is up to the implementation, although
it is RECOMMENDED to implement case #1.
In case #2, the server MUST send a <conflict/> stream error to the
current resource, terminate the XML stream and underlying TCP
connection for the current resource, and return an IQ stanza of type
"result" (indicating success) to the newly-requested resource.
In case #3, the server MUST send a <conflict/> stanza error to the
newly-requested resource but maintain the XML stream for that
connection so that the newly-requested resource has an opportunity to
negotiate a non-conflicting resource identifier before sending
another request for resource binding.
8.5. Binding Multiple Resources
A server MAY support binding of multiple resources to the same
stream. This functionality is desirable in certain environments
(e.g., for devices that are unable to open more than one TCP
connection or when a machine runs a local XMPP client daemon that is
used by multiple applications).
8.5.1. Support
If a server supports binding of multiple resources to a stream, it
MUST enable a client to unbind resources. A server that supports
unbinding MUST also support binding of multiple resources. Thus a
client can discover whether a server supports binding of multiple
resources by determining if the server advertises a stream feature of
<unbind/>, as follows.
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S: <stream:features>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<required/>
</bind>
<unbind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/>
</stream:features>
8.5.2. Binding an Additional Resource
A connected client binds an additional resource by following the
protocol for binding of the original resource, i.e., by sending an IQ
stanza of type "set" containing a <bind/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-bind' namespace (either empty to request
server generation of the resource identifier or containing a
<resource/> element with XML character data to request client
generation of the resource identifier).
8.5.3. Unbinding a Resource
8.5.3.1. Success Case
A client unbinds a resource by sending an IQ stanza of type "set"
containing an <unbind/> element qualified by the
'urn:ietf:params:xml:ns:xmpp-bind' namespace, which in turn contains
a child element of <resource/> whose XML character data specifies the
resource to be unbound:
C: <iq id='unbind_1' type='set'>
<unbind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<resource>someresource</resource>
</unbind>
</iq>
If no error occurs, the server MUST unbind the resource and no longer
accept stanzas whose 'from' address specifies the full JID associated
with that resource.
S: <iq id='unbind_1' type='result'/>
When a client unbinds the only resource associated with the stream,
the server SHOULD close the stream and terminate the TCP connection.
S: <iq id='unbind_1' type='result'/>
S: <stream:stream>
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8.5.3.2. Error Cases
8.5.3.2.1. Unbind Not Supported
If the server does not understand the <unbind/> element, it MUST
return a stanza error, which SHOULD be <bad-request/>.
S: <iq id='unbind_1' type='error'>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
8.5.3.2.2. No Such Resource
If there is no such resource for that stream, the server MUST return
an error of <item-not-found/>.
S: <iq id='unbind_1' type='error'>
<error type='cancel'>
<item-not-found xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
8.5.4. From Addresses
When a client binds multiple resources to the same stream, proper
management of 'from' addresses is imperative. In particular, a
client MUST specify a 'from' address on every stanza it sends over a
stream to which it has bound multiple resources, where the 'from'
address is the full JID (<node@domain.tld/resource>) associated with
the relevant resource. If a client does not specify a 'from' address
on a stanza it sends over a stream to which it has bound multiple
resources, the server MUST return the stanza to the client with an
<unknown-sender/> stanza error.
C: <message to='romeo@example.net'>
<body>Wherefore art thou?</body>
</message>
S: <message from='romeo@example.net'
type='error'>
<body>Wherefore art thou?</body>
<error type='modify'>
<unknown-sender xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</message>
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Naturally, the rules regarding validation of asserted 'from'
addresses still apply (see Section 11).
9. XML Stanzas
After a client has connected to a server or two servers have
connected to each other, either party can send XML stanzas over the
negotiated stream. Three kinds of XML stanza are defined for the
'jabber:client' and 'jabber:server' namespaces: <message/>,
<presence/>, and <iq/>. In addition, there are five common
attributes for these stanza types. These common attributes, as well
as the basic semantics of the three stanza types, are defined herein;
more detailed information regarding the syntax of XML stanzas for
instant messaging and presence applications is provided in [XMPP-IM],
and for other applications in the relevant XMPP extension
specifications.
An XML stanza is the basic unit of meaning in XMPP. A server MUST
NOT process a partial stanza and a server MUST NOT attach meaning to
the transmission timing of any child element within a stanza.
Support for the XML stanza syntax and semantics defined herein is
REQUIRED in XMPP client and server implementations.
9.1. Common Attributes
The following five attributes are common to message, presence, and IQ
stanzas.
9.1.1. to
The 'to' attribute specifies the JID of the intended recipient for
the stanza.
<message to='romeo@example.net'>
<body>Art thou not Romeo, and a Montague?</body>
</message>
For information about server processing of inbound and outbound XML
stanzas based on the nature of the 'to' address, refer to Section 11.
9.1.1.1. Client-to-Server Streams
The following rules apply to the 'to' attribute in the context of XML
streams qualified by the 'jabber:client' namespace (i.e., client-to-
server streams).
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1. A stanza with a specific intended recipient MUST possess a 'to'
attribute.
2. A stanza sent from a client to a server for direct processing by
the server (e.g., presence sent to the server for broadcasting to
other entities) SHOULD NOT possess a 'to' attribute.
9.1.1.2. Server-to-Server Streams
The following rules apply to the 'to' attribute in the context of XML
streams qualified by the 'jabber:server' namespace (i.e., server-to-
server streams).
1. A stanza MUST possess a 'to' attribute; if a server receives a
stanza that does not meet this restriction, it MUST generate an
<improper-addressing/> stream error and terminate both the XML
stream and the underlying TCP connection with the offending
server.
9.1.2. from
The 'from' attribute specifies the JID of the sender.
<message from='juliet@example.com/balcony'
to='romeo@example.net'>
<body>Art thou not Romeo, and a Montague?</body>
</message>
9.1.2.1. Client-to-Server Streams
The following rules apply to the 'from' attribute in the context of
XML streams qualified by the 'jabber:client' namespace (i.e., client-
to-server streams).
1. When the server receives an XML stanza from a client and the
stanza does not include a 'from' attribute, the server MUST add a
'from' attribute to the stanza, where the value of the 'from'
attribute is the full JID (<node@domain/resource>) determined by
the server for the connected resource that generated the stanza
(see Section 3.5), or the bare JID (<node@domain>) in the case of
subscription-related presence stanzas (see [XMPP-IM]).
2. When the server receives an XML stanza from a client and the
stanza includes a 'from' attribute, the server MUST either (a)
validate that the value of the 'from' attribute provided by the
client is that of a connected resource for the associated entity
or (b) override the provided 'from' attribute by adding a 'from'
attribute as specified under Rule #1.
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3. When the server generates a stanza from the server for delivery
to the client on behalf of the account of the connected client
(e.g., in the context of data storage services provided by the
server on behalf of the client), the stanza MUST either (a) not
include a 'from' attribute or (b) include a 'from' attribute
whose value is the account's bare JID (<node@domain>).
4. When the server generates a stanza from the server itself for
delivery to the client, the stanza MUST include a 'from'
attribute whose value is the mere domain (<domain>) of the
server.
5. A server MUST NOT send to the client a stanza without a 'from'
attribute if the stanza was not generated by the server (e.g., if
it was generated by another client or another server); therefore,
when a client receives a stanza that does not include a 'from'
attribute, it MUST assume that the stanza is from the server to
which the client is connected.
9.1.2.2. Server-to-Server Streams
The following rules apply to the 'from' attribute in the context of
XML streams qualified by the 'jabber:server' namespace (i.e., server-
to-server streams).
1. A stanza MUST possess a 'from' attribute; if a server receives a
stanza that does not meet this restriction, it MUST generate an
<improper-addressing/> stream error and terminate the underlying
TCP connection.
2. The domain identifier portion of the JID contained in the 'from'
attribute MUST match the hostname of the sending server (or any
validated domain thereof, such as a validated local domain hosted
by the sending server) as communicated in the SASL negotiation
(see Section 7), server dialback (see [XEP-0220], or similar
means; if a server receives a stanza that does not meet this
restriction, it MUST generate an <invalid-from/> stream error and
terminate the underlying TCP connection.
Enforcement of these rules helps to prevent a denial of service
attack launched from a rogue server.
9.1.3. id
The 'id' attribute MAY be used by a sending entity for internal
tracking of stanzas that it sends and receives (especially for
tracking the request-response interaction inherent in the semantics
of IQ stanzas). It is OPTIONAL for the value of the 'id' attribute
to be unique globally, within a domain, or within a stream. The
semantics of IQ stanzas impose additional restrictions; see
Section 9.2.3.
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9.1.4. type
The 'type' attribute specifies detailed information about the purpose
or context of the message, presence, or IQ stanza. The particular
allowable values for the 'type' attribute vary depending on whether
the stanza is a message, presence, or IQ stanza. The defined values
for message and presence stanzas are specific to instant messaging
and presence applications and therefore are specified in [XMPP-IM],
whereas the values for IQ stanzas specify the role of an IQ stanza in
a structured request-response exchange and thus are specified under
Section 9.2.3. The only 'type' value common to all three stanzas is
"error"; see Section 9.3.
9.1.5. xml:lang
A stanza SHOULD possess an 'xml:lang' attribute (as defined in
Section 2.12 of [XML]) if the stanza contains XML character data that
is intended to be presented to a human user (as explained in
[CHARSET], "internationalization is for humans"). The value of the
'xml:lang' attribute specifies the default language of any such
human-readable XML character data.
<presence from='romeo@example.net/orchard' xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
</presence>
The value of the 'xml:lang' attribute MAY be overridden by the 'xml:
lang' attribute of a specific child element.
<presence from='romeo@example.net/orchard' xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
<status xml:lang='cs'>Dvořím se Julii</status>
</presence
If an outbound stanza generated by a client does not possess an 'xml:
lang' attribute, the client's server MAY add an 'xml:lang' attribute
whose value is that specified for the stream as defined under
Section 5.3.
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C: <presence from='romeo@example.net/orchard'>
<show>dnd</show>
<status>Wooing Juliet</status>
</presence>
S: <presence from='romeo@example.net/orchard'
to='juliet@example.com/chamber'
xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
</presence>
If an inbound stanza received does not possess an 'xml:lang'
attribute, an implementation MUST assume that the default language is
that specified for the stream as defined under Section 5.3.
The value of the 'xml:lang' attribute MUST conform to the NMTOKEN
datatype (as defined in Section 2.3 of [XML]) and MUST conform to the
format defined in [LANGTAGS].
A server MUST NOT modify or delete 'xml:lang' attributes on stanzas
it receives from other entities.
9.2. Basic Semantics
9.2.1. Message Semantics
The <message/> stanza can be seen as a "push" mechanism whereby one
entity pushes information to another entity, similar to the
communications that occur in a system such as email. All message
stanzas SHOULD possess a 'to' attribute that specifies the intended
recipient of the message; upon receiving such a stanza, a server
SHOULD route or deliver it to the intended recipient (see Section 11
for general routing and delivery rules related to XML stanzas).
9.2.2. Presence Semantics
The <presence/> stanza can be seen as a specialized broadcast or
"publish-subscribe" mechanism, whereby multiple entities receive
information about an entity to which they have subscribed (in this
case, network availability information). In general, a publishing
entity (client) SHOULD send a presence stanza with no 'to' attribute,
in which case the server to which the entity is connected SHOULD
broadcast or multiplex that stanza to all subscribing entities.
However, a publishing entity MAY also send a presence stanza with a
'to' attribute, in which case the server SHOULD route or deliver that
stanza to the intended recipient. See Section 11 for general routing
and delivery rules related to XML stanzas, and [XMPP-IM] for rules
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specific to presence applications.
9.2.3. IQ Semantics
Info/Query, or IQ, is a request-response mechanism, similar in some
ways to [HTTP]. The semantics of IQ enable an entity to make a
request of, and receive a response from, another entity. The data
content of the request and response is defined by the schema or other
structural definition associated with the XML namespace that
qualifies the direct child element of the IQ element (see
Section 9.4), and the interaction is tracked by the requesting entity
through use of the 'id' attribute. Thus, IQ interactions follow a
common pattern of structured data exchange such as get/result or set/
result (although an error may be returned in reply to a request if
appropriate):
Requesting Responding
Entity Entity
---------- ----------
| |
| <iq id='1' type='get'> |
| [ ... payload ... ] |
| </iq> |
| -------------------------> |
| |
| <iq id='1' type='result'> |
| [ ... payload ... ] |
| </iq> |
| <------------------------- |
| |
| <iq id='2' type='set'> |
| [ ... payload ... ] |
| </iq> |
| -------------------------> |
| |
| <iq id='2' type='error'> |
| [ ... condition ... ] |
| </iq> |
| <------------------------- |
| |
In order to enforce these semantics, the following rules apply:
1. The 'id' attribute is REQUIRED for IQ stanzas.
2. The 'type' attribute is REQUIRED for IQ stanzas. The value MUST
be one of the following:
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* get -- The stanza is a request for information or
requirements.
* set -- The stanza provides required data, sets new values, or
replaces existing values.
* result -- The stanza is a response to a successful get or set
request.
* error -- An error has occurred regarding processing or
delivery of a previously-sent get or set (see Section 9.3).
3. An entity that receives an IQ request of type "get" or "set" MUST
reply with an IQ response of type "result" or "error". The
response MUST preserve the 'id' attribute of the request.
4. 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, 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).
5. An IQ stanza of type "get" or "set" MUST contain one and only one
child element that specifies the semantics of the particular
request.
6. An IQ stanza of type "result" MUST include zero or one child
elements.
7. An IQ stanza of type "error" MAY include the child element
contained in the associated "get" or "set" and MUST include an
<error/> child; for details, see Section 9.3.
9.3. Stanza Errors
Stanza-related errors are handled in a manner similar to stream
errors (Section 5.8). Unlike stream errors, stanza errors are
recoverable; therefore they do not result in termination of the XML
stream and underlying TCP connection. Instead, the entity that
discovers the error condition returns an ERROR STANZA to the sender,
i.e., a stanza of the same kind (message, presence, or IQ) whose
'type' attribute is set to a value of "error" and which contains an
<error/> child element that specifies the error condition. The
specified error condition provides a hint regarding actions that the
sender can take to remedy the error.
9.3.1. Rules
The following rules apply to stanza errors:
1. The receiving or processing entity that detects an error
condition in relation to a stanza SHOULD return an error stanza
(and MUST do so for IQ stanzas).
2. The entity that generates an error stanza MAY include the
original XML sent so that the sender can inspect and, if
necessary, correct the XML before attempting to resend.
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3. An error stanza MUST contain an <error/> child element.
4. An <error/> child MUST NOT be included if the 'type' attribute
has a value other than "error" (or if there is no 'type'
attribute).
5. An entity that receives an error stanza MUST NOT respond to the
stanza with a further error stanza; this helps to prevent
looping.
9.3.2. Syntax
The syntax for stanza-related errors is:
<stanza-kind from='intended-recipient' to='sender' type='error'>
[OPTIONAL to include sender XML here]
<error type='error-type'>
<defined-condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
[<text xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'
xml:lang='langcode'>
OPTIONAL descriptive text
</text>]
[OPTIONAL application-specific condition element]
</error>
</stanza-kind>
The "stanza-kind" is one of message, presence, or iq.
The value of the <error/> element's 'type' attribute MUST be one of
the following:
o cancel -- do not retry (the error cannot be remedied)
o continue -- proceed (the condition was only a warning)
o modify -- retry after changing the data sent
o auth -- retry after providing credentials
o wait -- retry after waiting (the error is temporary)
The <error/> element:
o MUST contain a child element corresponding to one of the defined
stanza error conditions specified; this element MUST be qualified
by the 'urn:ietf:params:xml:ns:xmpp-stanzas' namespace.
o MAY contain a <text/> child element containing XML character data
that describes the error in more detail; this element MUST be
qualified by the 'urn:ietf:params:xml:ns:xmpp-stanzas' namespace
and SHOULD possess an 'xml:lang' attribute specifying the natural
language of the XML character data.
o MAY contain a child element for an application-specific error
condition; this element MUST be qualified by an application-
defined namespace, and its structure is defined by that namespace.
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The <text/> element is OPTIONAL. If included, it SHOULD be used only
to provide descriptive or diagnostic information that supplements the
meaning of a defined condition or application-specific condition. It
SHOULD NOT be interpreted programmatically by an application. It
SHOULD NOT be used as the error message presented to a user, but MAY
be shown in addition to the error message associated with the
included condition element (or elements).
Finally, to maintain backward compatibility, the schema for the
default namespace (specified in [XMPP-IM]) allows the optional
inclusion of a 'code' attribute on the <error/> element; for details,
see [XEP-0086].
9.3.3. Defined Conditions
The following conditions are defined for use in stanza errors.
9.3.3.1. bad-request
The sender has sent a stanza containing XML that does not conform to
the appropriate schema or that cannot be processed (e.g., an IQ
stanza that includes an unrecognized value of the 'type' attribute);
the associated error type SHOULD be "modify".
C: <iq from='juliet@example.com/balcony'
id='some-id'
to='example.com'
type='subscribe'>
<ping xmlns='urn:xmpp:ping'/>
</iq>
S: <iq from='example.com'
id='some-id'
to='juliet@example.com/balcony'
type='error'>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
9.3.3.2. conflict
Access cannot be granted because an existing resource exists with the
same name or address; the associated error type SHOULD be "cancel".
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C: <iq id='bind_2' type='set'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<resource>balcony</resource>
</bind>
</iq>
S: <iq id='bind_2' type='error'>
<error type='cancel'>
<conflict xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
9.3.3.3. feature-not-implemented
The feature represented in the XML stanza is not implemented by the
recipient or server and therefore the stanza cannot be processed; the
associated error type SHOULD be "cancel" or "modify".
C: <iq from='juliet@example.com/balcony'
id='subscriptions1'
to='pubsub.example.com'
type='get'>
<pubsub xmlns='http://jabber.org/protocol/pubsub'>
<subscriptions/>
</pubsub>
</iq>
E: <iq from='pubsub.example.com
id='subscriptions1'
to='juliet@example.com/balcony'
type='error'>
<error type='cancel'>
<feature-not-implemented
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<unsupported
xmlns='http://jabber.org/protocol/pubsub#errors'
feature='retrieve-subscriptions'/>
</error>
</iq>
9.3.3.4. forbidden
The requesting entity does not possess the required permissions to
perform the action; the associated error type SHOULD be "auth".
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C: <presence
from='juliet@example.com/balcony'
to='characters@chat.example.com/JulieC'>
<x xmlns='http://jabber.org/protocol/muc'/>
</presence>
E: <presence
from='characters@chat.example.com/JulieC'
to='juliet@example.com/balcony'
type='error'>
<error type='auth'>
<forbidden xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</presence>
9.3.3.5. gone
The recipient or server can no longer be contacted at this address
(the error stanza MAY contain a new address in the XML character data
of the <gone/> element); the associated error type SHOULD be "cancel"
or "modify".
C: <presence
from='juliet@example.com/balcony'
to='characters@chat.example.com/JulieC'>
<x xmlns='http://jabber.org/protocol/muc'/>
</presence>
E: <presence
from='characters@chat.example.com/JulieC'
to='juliet@example.com/balcony'
type='error'>
<error type='modify'>
<gone xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
conference.example.com
</gone>
</error>
</presence>
9.3.3.6. internal-server-error
<internal-server-error/> -- the server could not process the stanza
because of a misconfiguration or an otherwise-undefined internal
server error; the associated error type SHOULD be "wait" or "cancel".
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C: <presence
from='juliet@example.com/balcony'
to='characters@chat.example.com/JulieC'>
<x xmlns='http://jabber.org/protocol/muc'/>
</presence>
E: <presence
from='characters@chat.example.com/JulieC'
to='juliet@example.com/balcony'
type='error'>
<error type='wait'>
<internal-server-error
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</presence>
9.3.3.7. item-not-found
The addressed JID or item requested cannot be found; the associated
error type SHOULD be "cancel" or "modify".
C: <iq id='unbind_1' type='set'>
<unbind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<resource>someresource</resource>
</unbind>
</iq>
S: <iq id='unbind_1' type='error'>
<error type='cancel'>
<item-not-found xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
An application MUST NOT return this error if doing so would provide
information about the intended recipient's network availability to an
entity that is not authorized to know such information; instead it
SHOULD return a <service-unavailable/> error.
9.3.3.8. jid-malformed
The sending entity has provided or communicated an XMPP address
(e.g., a value of the 'to' attribute) or aspect thereof (e.g., an
XMPP resource identifier) that does not adhere to the syntax defined
under Section 3; the associated error type SHOULD be "modify".
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C: <presence
from='juliet@example.com/balcony'
to='ch@r@cters@chat.example.com/JulieC'>
<x xmlns='http://jabber.org/protocol/muc'/>
</presence>
E: <presence
from='ch@r@cters@chat.example.com/JulieC'
to='juliet@example.com/balcony'
type='error'>
<error type='modify'>
<jid-malformed
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</presence>
9.3.3.9. not-acceptable
The recipient or server understands the request but is refusing to
process it because it does not meet criteria defined by the recipient
or server (e.g., a local policy regarding stanza size limits or
acceptable words in messages); the associated error type SHOULD be
"modify".
C: <message to='juliet@example.com' id='foo'>
<body>[ ... the-emacs-manual ... ]</body>
</message>
S: <message from='juliet@example.com' id='foo'>
<error type='modify'>
<not-acceptable
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</message>
9.3.3.10. not-allowed
The recipient or server does not allow any entity to perform the
action (e.g., sending to entities at a blacklisted domain); the
associated error type SHOULD be "cancel".
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C: <presence
from='juliet@example.com/balcony'
to='characters@chat.example.com/JulieC'>
<x xmlns='http://jabber.org/protocol/muc'/>
</presence>
E: <presence
from='characters@chat.example.com/JulieC'
to='juliet@example.com/balcony'>
<error type='cancel'>
<not-allowed xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</presence>
9.3.3.11. not-authorized
The sender must provide proper credentials before being allowed to
perform the action, or has provided improper credentials; the
associated error type SHOULD be "auth".
C: <presence
from='juliet@example.com/balcony'
to='characters@chat.example.com/JulieC'>
<x xmlns='http://jabber.org/protocol/muc'/>
</presence>
E: <presence
from='characters@chat.example.com/JulieC'
to='juliet@example.com/balcony'>
<error type='auth'>
<not-authorized xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</presence>
9.3.3.12. not-modified
The item requested has not changed since it was last requested; the
associated error type SHOULD be "continue".
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C: <iq from='juliet@capulet.com/balcony'
id='roster2'
type='get'>
<query xmlns='jabber:iq:roster'>
<headers xmlns='http://jabber.org/protocol/shim'>
<header name='If-None-Match'>some-long-opaque-string</header>
</headers>
</query>
</iq>
S: <iq type='error'
to='juliet@capulet.com/balcony'
id='roster2'>
<query xmlns='jabber:iq:roster'>
<headers xmlns='http://jabber.org/protocol/shim'>
<header name='If-None-Match'>some-long-opaque-string</header>
</headers>
</query>
<error type='modify'>
<not-modified xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
9.3.3.13. payment-required
The requesting entity is not authorized to access the requested
service because payment is required; the associated error type SHOULD
be "auth".
C: <iq from='romeo@example.net/foo'
id='items1'
to='pubsub.example.com'
type='get'>
<pubsub xmlns='http://jabber.org/protocol/pubsub'>
<items node='my_musings'/>
</pubsub>
</iq>
E: <iq from='pubsub.example.com'
id='items1'
to='romeo@example.net/foo'
type='error'>
<error type='auth'>
<payment-required
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
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9.3.3.14. recipient-unavailable
The intended recipient is temporarily unavailable; the associated
error type SHOULD be "wait".
C: <presence
from='juliet@example.com/balcony'
to='characters@chat.example.com/JulieC'>
<x xmlns='http://jabber.org/protocol/muc'/>
</presence>
E: <presence
from='characters@chat.example.com/JulieC'
to='juliet@example.com/balcony'>
<error type='wait'>
<recipient-unavailable
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</presence>
An application MUST NOT return this error if doing so would provide
information about the intended recipient's network availability to an
entity that is not authorized to know such information; instead it
SHOULD return a <service-unavailable/> error.
9.3.3.15. redirect
The recipient or server is redirecting requests for this information
to another entity, typically in a temporary fashion (the error stanza
SHOULD contain the alternate address, which SHOULD be a valid JID, in
the XML character data of the <redirect/> element); the associated
error type SHOULD be "modify".
C: <presence
from='juliet@example.com/balcony'
to='characters@chat.example.com/JulieC'>
<x xmlns='http://jabber.org/protocol/muc'/>
</presence>
E: <presence
from='characters@chat.example.com/JulieC'
to='juliet@example.com/balcony'
type='error'>
<error type='modify'>
<redirect xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
characters@conference.example.org
</redirect>
</error>
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</presence>
9.3.3.16. registration-required
The requesting entity is not authorized to access the requested
service because prior registration is required; the associated error
type SHOULD be "auth".
C: <presence
from='juliet@example.com/balcony'
to='characters@chat.example.com/JulieC'>
<x xmlns='http://jabber.org/protocol/muc'/>
</presence>
E: <presence
from='characters@chat.example.com/JulieC'
to='juliet@example.com/balcony'>
<error type='auth'>
<registration-required
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</presence>
9.3.3.17. remote-server-not-found
A remote server or service specified as part or all of the JID of the
intended recipient does not exist; the associated error type SHOULD
be "cancel".
C: <presence
from='juliet@example.com/balcony'
to='characters@chat.example.com/JulieC'>
<x xmlns='http://jabber.org/protocol/muc'/>
</presence>
E: <presence
from='characters@chat.example.com/JulieC'
to='juliet@example.com/balcony'>
<error type='wait'>
<remote-server-not-found
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</presence>
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9.3.3.18. remote-server-timeout
A remote server or service specified as part or all of the JID of the
intended recipient (or required to fulfill a request) could not be
contacted within a reasonable amount of time; the associated error
type SHOULD be "wait".
C: <presence
from='juliet@example.com/balcony'
to='characters@chat.example.com/JulieC'>
<x xmlns='http://jabber.org/protocol/muc'/>
</presence>
E: <presence
from='characters@chat.example.com/JulieC'
to='juliet@example.com/balcony'>
<error type='wait'>
<remote-server-timeout
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</presence>
9.3.3.19. resource-constraint
The server or recipient lacks the system resources necessary to
service the request; the associated error type SHOULD be "wait".
C: <iq from='romeo@example.net/foo'
id='items1'
to='pubsub.example.com'
type='get'>
<pubsub xmlns='http://jabber.org/protocol/pubsub'>
<items node='my_musings'/>
</pubsub>
</iq>
E: <iq from='pubsub.example.com'
id='items1'
to='romeo@example.net/foo'
type='error'>
<error type='wait'>
<resource-constraint
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
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9.3.3.20. service-unavailable
The server or recipient does not currently provide the requested
service; the associated error type SHOULD be "cancel".
C: <message from='romeo@example.net/foo'
to='juliet@example.com'>
<body>Hello?</body>
</message>
S: <message from='juliet@example.com/foo'
to='romeo@example.net'>
<error type='cancel'>
<service-unavailable
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</message>
An application SHOULD return a <service-unavailable/> error instead
of <item-not-found/> or <recipient-unavailable/> if sending one of
the latter errors would provide information about the intended
recipient's network availability to an entity that is not authorized
to know such information.
9.3.3.21. subscription-required
The requesting entity is not authorized to access the requested
service because a subscription is required; the associated error type
SHOULD be "auth".
C: <message
from='romeo@example.net/orchard'
to='playbot@shakespeare.example.com'
<body>help</body>
</message>
E: <message
from='playbot@shakespeare.example.com'
to='romeo@example.net/orchard'
type='error'>
<error type='auth'>
<subscription-required
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</message>
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9.3.3.22. undefined-condition
The error condition is not one of those defined by the other
conditions in this list; any error type may be associated with this
condition, and it SHOULD be used only in conjunction with an
application-specific condition.
C: <message
from='northumberland@shakespeare.lit'
id='richard2-4.1.247'
to='kingrichard@royalty.england.lit'>
<body>My lord, dispatch; read o'er these articles.</body>
<amp xmlns='http://jabber.org/protocol/amp'>
<rule action='notify'
condition='deliver'
value='stored'/>
</amp>
S: <message from='example.org'
id='amp1'
to='northumberland@example.net/field'
type='error'>
<amp xmlns='http://jabber.org/protocol/amp'
from='kingrichard@example.org'
status='error'
to='northumberland@example.net/field'>
<rule action='error'
condition='deliver'
value='stored'/>
</amp>
<error type='modify'>
<undefined-condition
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<failed-rules xmlns='http://jabber.org/protocol/amp#errors'>
<rule action='error'
condition='deliver'
value='stored'/>
</failed-rules>
</error>
</message>
9.3.3.23. unexpected-request
The recipient or server understood the request but was not expecting
it at this time (e.g., the request was out of order); the associated
error type SHOULD be "wait" or "modify".
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C: <iq from='romeo@example.net/foo'
id='unsub1'
to='pubsub.example.com'
type='set'>
<pubsub xmlns='http://jabber.org/protocol/pubsub'>
<unsubscribe
node='my_musings'
jid='romeo@example.net'/>
</pubsub>
</iq>
E: <iq from='pubsub.example.com'
id='unsub1'
to='romeo@example.net/foo'
type='error'>
<error type='cancel'>
<unexpected-request
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<not-subscribed
xmlns='http://jabber.org/protocol/pubsub#errors'/>
</error>
</iq>
9.3.3.24. unknown-sender
The stanza 'from' address specified by a connected client is not
valid for the stream (e.g., the stanza does not include a 'from'
address when multiple resources are bound to the stream); the
associated error type SHOULD be "modify".
C: <message to='romeo@example.net'>
<body>Wherefore art thou?</body>
</message>
S: <message from='romeo@example.net'
type='error'>
<body>Wherefore art thou?</body>
<error type='modify'>
<unknown-sender xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</message>
9.3.4. Application-Specific Conditions
As noted, an application MAY provide application-specific stanza
error information by including a properly-namespaced child in the
error element. The application-specific element SHOULD supplement or
further qualify a defined element. Thus, the <error/> element will
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contain two or three child elements:
<iq id='some-id' type='error'>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<too-many-parameters xmlns='application-ns'/>
</error>
</iq>
<message type='error' id='another-id'>
<error type='modify'>
<undefined-condition
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<text xml:lang='en'
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
[ ... application-specific information ... ]
</text>
<special-application-condition xmlns='application-ns'/>
</error>
</message>
9.4. Extended Content
While the message, presence, and IQ stanzas provide basic semantics
for messaging, availability, and request-response interactions, XMPP
uses XML namespaces (see [XML-NAMES] to extend the basic stanza
syntax for the purpose of providing additional functionality. Thus a
message or presence stanza MAY contain one or more optional child
elements specifying content that extends the meaning of the message
(e.g., an XHTML-formatted version of the message body as described in
[XEP-0071]), and an IQ stanza of type "get" or "set" MUST contain one
such child element. This child element MAY have any name and MUST
possess an 'xmlns' namespace declaration (other than "jabber:client",
"jabber:server", or "http://etherx.jabber.org/streams") that defines
all data contained within the child element. Such a child element is
said to be EXTENDED CONTENT and its namespace name is said to be an
EXTENDED NAMESPACE.
Support for any given extended namespace is OPTIONAL on the part of
any implementation. If an entity does not understand such a
namespace, the entity's expected behavior depends on whether the
entity is (1) the recipient or (2) an entity that is routing the
stanza to the recipient:
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Recipient: If a recipient receives a stanza that contains a child
element it does not understand, it SHOULD silently ignore that
particular XML data, i.e., it SHOULD not process it or present it
to a user or associated application (if any). In particular:
* If an entity receives a message or presence stanza that
contains XML data qualified by a namespace it does not
understand, the portion of the stanza that qualified by the
unknown namespace SHOULD be ignored.
* If an entity receives a message stanza whose only child element
is qualified by a namespace it does not understand, it MUST
ignore the entire stanza.
* If an entity receives an IQ stanza of type "get" or "set"
containing a child element qualified by a namespace it does not
understand, the entity SHOULD return an IQ stanza of type
"error" with an error condition of <service-unavailable/>.
Router: If a routing entity (typically a server) handles a stanza
that contains a child element it does not understand, it SHOULD
ignore the associated XML data by routing or delivering it
untouched to the recipient.
10. Examples
10.1. Client-to-Server
The following examples show the XMPP data flow for a client
negotiating an XML stream with a server, exchanging XML stanzas, and
closing the negotiated stream. The server is "example.com", the
server requires use of TLS, the client authenticates via the SASL
DIGEST-MD5 mechanism as "juliet@example.com", and the client binds a
server-generated resource to the stream. It is assumed that before
sending the initial stream header, the client has already resolved an
SRV record of _xmpp-client._tcp.example.com and has opened a TCP
connection to the advertised port at the resolved IP address.
Note: The alternate steps shown are provided only to illustrate the
protocol for failure cases; they are not exhaustive and would not
necessarily be triggered by the data sent in the examples.
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10.1.1. TLS
Step 1: Client initiates stream to server:
C: <stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
Step 2: Server responds by sending a stream header to client:
S: <stream:stream
from='example.com'
id='t7AMCin9zjMNwQKDnplntZPIDEI='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
Step 3: Server sends stream features to client (STARTTLS extension
only at this point):
S: <stream:features>
<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'>
<required/>
</starttls>
</stream:features>
Step 4: Client sends STARTTLS command to server:
C: <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
Step 5: Server informs client that it is allowed to proceed:
S: <proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
Step 5 (alt): Server informs client that TLS negotiation has failed
and closes both XML stream and TCP connection:
S: <failure xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
S: </stream:stream>
Step 6: Client and server attempt to complete TLS negotiation over
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the existing TCP connection (see [TLS] for details).
Step 7: If TLS negotiation is successful, client initiates a new
stream to server:
C: <stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
Step 7 (alt): If TLS negotiation is unsuccessful, server closes TCP
connection.
10.1.2. SASL
Step 8: Server responds by sending a stream header to client along
with any available stream features:
S: <stream:stream
from='example.com'
id='vgKi/bkYME8OAj4rlXMkpucAqe4='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
S: <stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
<required/>
</mechanisms>
</stream:features>
Step 9: Client selects an authentication mechanism, in this case
[DIGEST-MD5] with an empty authorization identity ("="):
C: <auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
mechanism='DIGEST-MD5'>=</auth>
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Step 10: Server sends a [BASE64] encoded challenge to client:
S: <challenge xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
cmVhbG09ImV4YW1wbGUuY29tIixub25jZT0iT0E2TUc5dEVRR20yaGgiLHFvcD0i
YXV0aCIsY2hhcnNldD11dGYtOCxhbGdvcml0aG09bWQ1LXNlc3MK
</challenge>
The decoded challenge is:
realm="example.com",nonce="OA6MG9tEQGm2hh",
qop="auth",charset=utf-8,algorithm=md5-sess
Note: When the server sends a DIGEST-MD5 challenge to the client, the
qop list must be quoted since it is a list rather than a single item
(even if there is only one item in the list); however, when the
client sends its response to the server, the qop must not be quoted
since it is a single item rather than a list.
Step 10 (alt): Server returns error to client:
S: <failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<temporary-auth-failure/>
</failure>
S: </stream:stream>
Step 11: Client sends a [BASE64] encoded response to the challenge:
C: <response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
dXNlcm5hbWU9Imp1bGlldCIscmVhbG09ImV4YW1wbGUuY29tIixub25jZT0iT0E2
TUc5dEVRR20yaGgiLGNub25jZT0iT0E2TUhYaDZWcVRyUmsiLG5jPTAwMDAwMDAx
LHFvcD1hdXRoLGRpZ2VzdC11cmk9InhtcHAvZXhhbXBsZS5jb20iLHJlc3BvbnNl
PWQzODhkYWQ5MGQ0YmJkNzYwYTE1MjMyMWYyMTQzYWY3LGNoYXJzZXQ9dXRmLTgK
</response>
The decoded response is:
username="juliet",realm="example.com",
nonce="OA6MG9tEQGm2hh",cnonce="OA6MHXh6VqTrRk",
nc=00000001,qop=auth,digest-uri="xmpp/example.com",
response=d388dad90d4bbd760a152321f2143af7,charset=utf-8
Step 12: Server informs client of success and includes [BASE64]
encoded value for subsequent authentication:
S: <success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZAo=
</success>
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The decoded value for subsequent authentication is:
rspauth=ea40f60335c427b5527b84dbabcdfffd
Step 12 (alt): Server returns error to client:
S: <failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<not-authorized/>
</failure>
Step 13: Client initiates a new stream to server:
C: <stream:stream
from='juliet@example.com'
to='example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
10.1.3. Resource Binding
Step 14: Server responds by sending a stream header to client along
with supported features (in this case resource binding):
S: <stream:stream
from='example.com'
id='gPybzaOzBmaADgxKXu9UClbprp0='
to='juliet@example.com'
version='1.0'
xml:lang='en'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
S: <stream:features>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<required/>
</bind>
<unbind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/>
</stream:features>
Upon being so informed that resource binding is required, the client
MUST bind a resource to the stream; here we assume that the client
asks the server to generate a resource identifier on its behalf.
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Step 15: Client binds a resource:
C: <iq id='bind_1' type='set'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'/>
</iq>
Step 16: Server generates resource identifier and informs client of
successful resource binding:
S: <iq id='bind_1' type='result'>
<bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
<jid>
juliet@example.com/4db06f06-1ea4-11dc-aca3-000bcd821bfb
</jid>
</bind>
</iq>
10.1.4. Stanza Exchange
Now the client is allowed to send XML stanzas over the negotiated
stream.
C: <message
from='juliet@example.com/4db06f06-1ea4-11dc-aca3-000bcd821bfb'
to='romeo@example.net'
xml:lang='en'>
<body>Art thou not Romeo, and a Montague?</body>
</message>
If necessary, sender's server negotiates XML streams with intended
recipient's server (see Section 10.2).
The intended recipient replies and the message is delivered to the
client.
E: <message
from='romeo@example.net/63a6be96-1ea4-11dc-a38b-000bcd821cgc'
to='juliet@example.com/4db06f06-1ea4-11dc-aca3-000bcd821bfb'
xml:lang='en'>
<body>Neither, fair saint, if either thee dislike.</body>
</message>
The client may send and receive an unbounded number of subsequent XML
stanzas over the stream.
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10.1.5. Close
Desiring to send no further messages, the client closes the stream.
C: </stream:stream>
Consistent with the recommended stream closing handshake, server
closes stream as well:
S: </stream:stream>
Client now terminates the underlying TCP connection.
10.2. Server-to-Server Examples
The following examples show the data flow for a server negotiating an
XML stream with another server, exchanging XML stanzas, and closing
the negotiated stream. The initiating server ("Server1") is
example.com; the receiving server ("Server2") is example.net and it
requires use of TLS; example.com presents a certificate and
authenticates via the SASL EXTERNAL mechanism. It is assumed that
before sending the initial stream header, Server1 has already
resolved an SRV record of _xmpp-client._tcp.example.net and has
opened a TCP connection to the advertised port at the resolved IP
address.
Note: The alternate steps shown are provided only to illustrate the
protocol for failure cases; they are not exhaustive and would not
necessarily be triggered by the data sent in the examples.
10.2.1. TLS
Step 1: Server1 initiates stream to Server2:
S1: <stream:stream
from='example.com'
to='example.net'
version='1.0'
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'>
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Step 2: Server2 responds by sending a stream tag to Server1:
S2: <stream:stream
from='example.net'
id='hTiXkW+ih9k2SqdGkk/AZi0OJ/Q='
to='example.com'
version='1.0'
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'>
Step 3: Server2 sends stream features to Server1:
S2: <stream:features>
<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'>
<required/>
</starttls>
</stream:features>
Step 4: Server1 sends the STARTTLS command to Server2:
S1: <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
Step 5: Server2 informs Server1 that it is allowed to proceed:
S2: <proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
Step 5 (alt): Server2 informs Server1 that TLS negotiation has failed
and closes stream:
S2: <failure xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
S2: </stream:stream>
Step 6: Server1 and Server2 attempt to complete TLS negotiation via
TCP.
Step 7: If TLS negotiation is successful, Server1 initiates a new
stream to Server2:
S1: <stream:stream
from='example.com'
to='example.net'
version='1.0'
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'>
Step 7 (alt): If TLS negotiation is unsuccessful, Server2 closes TCP
connection.
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10.2.2. SASL
Step 8: Server2 responds by sending a stream header to Server1 along
with available stream features (including a preference for the SASL
EXTERNAL mechanism):
S2: <stream:stream
from='example.net'
id='RChdjlgj/TIBcbT9Keu31zDihH4='
to='example.com'
version='1.0'
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'>
S2: <stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>EXTERNAL</mechanism>
<mechanism>DIGEST-MD5</mechanism>
<required/>
</mechanisms>
</stream:features>
Step 9: Server1 selects the EXTERNAL mechanism, in this case with an
authorization identity encoded according to [BASE64]:
S1: <auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
mechanism='EXTERNAL'/>ZXhhbXBsZS5jb20K</auth>
The decoded authorization identity is "example.com".
Step 10: Server2 determines that the authorization identity provided
by Server1 matches the information in the presented certificate and
therefore returns success:
S2: <success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
Step 11 (alt): Server2 informs Server1 of failed authentication:
S2: <failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<not-authorized/>
</failure>
S2: </stream:stream>
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Step 12: Server1 initiates a new stream to Server2:
S1: <stream:stream
from='example.com'
to='example.net'
version='1.0'
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'>
Step 13: Server2 responds by sending a stream header to Server1 along
with any additional features (or, in this case, an empty features
element):
S2: <stream:stream
from='example.net'
id='MbbV2FeojySpUIP6J91qaa+TWHM='
to='example.com'
version='1.0'
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'>
S2: <stream:features/>
10.2.3. Stanza Exchange
Now Server1 is allowed to send XML stanzas to Server2 over the
negotiated stream; here we assume that the transferred stanzas are
those shown earlier for client-to-server communication.
Server1 sends XML stanza to Server2:
S1: <message from='juliet@example.com/balcony'
to='romeo@example.net'
xml:lang='en'>
<body>Art thou not Romeo, and a Montague?</body>
</message>
The intended recipient replies and the message is delivered from
Server2 to Server1.
Server2 sends XML stanza to Server1:
S2: <message from='romeo@example.net/orchard'
to='juliet@example.com/balcony'
xml:lang='en'>
<body>Neither, fair saint, if either thee dislike.</body>
</message>
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10.2.4. Close
Desiring to send no further messages, Server1 closes the stream. (In
practice, the stream would most likely remain open for some time,
since Server1 and Server2 do not immediately know if the stream will
be needed for further communication.)
S1: </stream:stream>
Consistent with the recommended stream closing handshake, Server2
closes stream as well:
S2: </stream:stream>
Server1 now terminates the underlying TCP connection.
11. Server Rules for Processing XML Stanzas
An XMPP server MUST ensure in-order processing of XML stanzas between
any two entities. This includes stanzas sent by a client to its
server for direct processing by the server (e.g., in-order processing
of a roster get and initial presence as decribed in [XMPP-IM]).
Beyond the requirement for in-order processing, each server
implementation will contain its own logic for processing stanzas it
receives. Such logic determines whether the server needs to ROUTE a
given stanza to another domain, DELIVER it to a local entity
(typically a connected client associated with a local account), or
HANDLE it directly within the server itself. The following rules
apply.
Note: Particular XMPP applications MAY specify delivery rules that
modify or supplement the following rules; for example, a set of
delivery rules for instant messaging and presence applications is
defined in [XMPP-IM].
11.1. No 'to' Address
11.1.1. Overview
If the stanza possesses no 'to' attribute, the server SHOULD handle
it directly on behalf of the entity that sent it. Because all
stanzas received from other servers MUST possess a 'to' attribute,
this rule applies only to stanzas received from a local entity (such
as a client) that is connected to the server.
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11.1.2. Message
If the server receives a message stanza with no 'to' attribute, it
SHOULD handle it directly, which may include returning an error to
the sending entity.
11.1.3. Presence
If the server receives a presence stanza with no 'to' attribute, it
SHOULD broadcast it to the entities that are subscribed to the
sending entity's presence, if applicable (the semantics of presence
broadcast for presence applications are defined in [XMPP-IM]).
11.1.4. IQ
If the server receives an IQ stanza of type "get" or "set" with no
'to' attribute, it MUST do the following:
1. If it understands the namespace that qualifies the content of the
stanza, it MUST either handle the stanza directly on behalf of
sending entity (where the meaning of "handle" is determined by
the semantics of the qualifying namespace) or return an
appropriate error to the sending entity.
2. If it does not understand the namespace that qualifies the
content of the stanza, it MUST return an error to the sending
entity, which SHOULD be <service-unavailable/>.
11.2. Local Domain
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute matches one of the configured hostnames of the
server itself, the server MUST do one of the following:
1. Handle the stanza itself.
2. Route the stanza to a specialized service that is responsible for
that local domain.
3. Return an error to the sender if the service providing the local
domain is not available.
11.3. Resource at Local Domain
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute matches a configured hostname of the server
itself and the JID contained in the 'to' attribute is of the form
<domain/resource>, the server (or a defined resource thereof) MUST
either handle the stanza as appropriate for the stanza kind or return
an error stanza to the sender.
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11.4. Node at Local Domain
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute matches a configured hostname of the server
itself and the JID contained in the 'to' attribute is a bare JID
(<node@domain>) or full JID (<node@domain/resource>), the server
SHOULD deliver the stanza to the intended recipient of the stanza as
represented by the JID contained in the 'to' attribute. The
following rules apply:
1. If the JID contains an XMPP resource identifier (i.e., is of the
form <node@domain/resource>) and there exists a connected
resource that exactly matches the full JID, the recipient's
server SHOULD deliver the stanza to that connection.
2. If the JID contains an XMPP resource identifier and there exists
no connected resource that exactly matches the full JID, the
recipient's server SHOULD return a <service-unavailable/> stanza
error to the sender.
3. If the JID is of the form <node@domain> and there exists at least
one connected resource for the node, the recipient's server
SHOULD deliver the stanza to at least one of the connected
resources if the stanza is a message or presence stanza and
SHOULD handle it directly on behalf of the node if the stanza is
an IQ stanza.
11.5. Foreign Domain
11.5.1. Overview
If the hostname of the domain identifier portion of the JID contained
in the 'to' attribute does not match one of the configured hostnames
of the server itself, the server SHOULD attempt to route the stanza
to the foreign domain (subject to local service provisioning and
security policies regarding inter-domain communication, since such
communication is optional for any given deployment). There are two
possible cases.
11.5.2. Existing Stream
If a server-to-server stream already exists between the two domains,
the sender's server shall attempt to route the stanza to the
authoritative server for the foreign domain over the existing stream.
11.5.3. No Existing Stream
If there exists no server-to-server stream between the two domains,
the sender's server shall proceed as follows:
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1. Resolve the hostname of the foreign domain (as defined under
Section 15.4).
2. Negotiate a server-to-server stream between the two domains (as
defined under Section 6 and Section 7).
3. Route the stanza to the authoritative server for the foreign
domain over the newly-established stream.
11.5.4. Error Handling
If routing to the intended recipient's server is unsuccessful, the
sender's server MUST return an error to the sender, which SHOULD be
<remote-server-not-found/> if resolution of the foreign domain is
unsuccessful and <remote-server-timeout/> if resolution succeeds but
streams cannot be negotiated.
If stream negotiation with the intended recipient's server is
successful but the foreign server cannot deliver the stanza to the
recipient, the foreign server shall return an error to the sender by
way of the sender's server.
12. XML Usage
12.1. Restrictions
XMPP is a simplified and specialized protocol for streaming XML
elements in order to exchange structured information in close to real
time. Because XMPP does not require the parsing of arbitrary and
complete XML documents, there is no requirement that XMPP needs to
support the full feature set of [XML]. In particular, the following
features of XML are prohibited in XMPP:
o comments (as defined in Section 2.5 of [XML])
o processing instructions (Section 2.6 therein)
o internal or external DTD subsets (Section 2.8 therein)
o internal or external entity references (Section 4.2 therein) with
the exception of predefined entities (Section 4.6 therein)
o character data or attribute values containing unescaped characters
that map to the predefined entities (Section 4.6 therein); such
characters MUST be escaped
An XMPP implementation MUST behave as follow with regard to these
features:
1. An XMPP implementation MUST NOT inject characters matching such
features into an XML stream.
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2. If an XMPP implementation receives characters matching such
features over an XML stream, it MUST return a stream error, which
SHOULD be <restricted-xml/> but MAY be <bad-format/>.
12.2. XML Namespace Names and Prefixes
XML namespaces (see [XML-NAMES]) are used within all XMPP-compliant
XML to create strict boundaries of data ownership. The basic
function of namespaces is to separate different vocabularies of XML
elements that are structurally mixed together. Ensuring that XMPP-
compliant XML is namespace-aware enables any allowable XML to be
structurally mixed with any data element within XMPP. Rules for XML
namespace names and prefixes are defined in the following
subsections.
12.2.1. Streams Namespace
A streams namespace declaration is REQUIRED in all XML stream headers
and the name of the streams namespace MUST be
'http://etherx.jabber.org/streams'. If this rule is violated, the
entity that receives the offending stream header MUST return a stream
error to the sending entity, which SHOULD be <invalid-namespace/> but
MAY be <bad-format/>.
The element names of the <stream/> element and its <features/> and
<error/> children MUST be qualified by the streams namespace prefix
in all instances. If this rule is violated, the entity that receives
the offending element MUST return a stream error to the sending
entity, which SHOULD be <bad-format/>.
An implementation SHOULD generate only the 'stream:' prefix for these
elements, and for historical reasons MAY accept only the 'stream:'
prefix. If an entity receives a stream header with a streams
namespace prefix it does not accept, it MUST return a stream error to
the sending entity, which SHOULD be <bad-namespace-prefix/> but MAY
be <bad-format/>.
12.2.2. Default Namespace
A default namespace declaration is REQUIRED and is used in all XML
streams in order to define the allowable first-level children of the
root stream element. This namespace declaration MUST be the same for
the initial stream and the response stream so that both streams are
qualified consistently. The default namespace declaration applies to
the stream and all stanzas sent within a stream (unless explicitly
qualified by another namespace or by the prefix of the streams
namespace).
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A server implementation MUST support the following two default
namespaces (for historical reasons, an implementation MAY support
only these two default namespaces):
o jabber:client -- this default namespace is declared when the
stream is used for communication between a client and a server
o jabber:server -- this default namespace is declared when the
stream is used for communication between two servers
A client implementation MUST support the 'jabber:client' default
namespace, and for historical reasons MAY support only that default
namespace.
If an implementation accepts a stream that is qualified by the
'jabber:client' or 'jabber:server' namespace, it MUST support the
common attributes (Section 9.1) and basic semantics (Section 9.2) of
all three core stanza types (message, presence, and IQ).
An implementation MUST NOT generate namespace prefixes for elements
qualified by the default namespace if the default namespace is
'jabber:client' or 'jabber:server'.
Note: The 'jabber:client' and 'jabber:server' namespaces are nearly
identical but are used in different contexts (client-to-server
communication for 'jabber:client' and server-to-server communication
for 'jabber:server'). The only difference between the two is that
the 'to' and 'from' attributes are OPTIONAL on stanzas sent over XML
streams qualified by the 'jabber:client' namespace, whereas they are
REQUIRED on stanzas sent over XML streams qualified by the 'jabber:
server' namespace.
12.2.3. Extended Namespaces
An EXTENDED NAMESPACE is an XML namespace (other than the default
namespace) that is used to qualify XML data contained within an XML
stanza. For example, in the following stanza, the extended namespace
is 'jabber:iq:roster':
<iq from='juliet@capulet.com/balcony'
id='roster1'
type='get'>
<query xmlns='jabber:iq:roster'/>
</iq>
An XML stanza MAY contain XML data qualified by more than one
extended namespace, either at the direct child level of the stanza
(for presence and message stanzas) or in any mix of levels (for all
stanzas).
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<presence from='juliet@capulet.com/balcony'>
<c xmlns='http://jabber.org/protocol/caps'
node='http://exodus.jabberstudio.org/caps'
ver='0.9'/>
<x xmlns='vcard-temp:x:update'>
<photo>sha1-hash-of-image</photo>
</x>
</presence>
<message to='juliet@capulet.com'>
<body>Hello?</body>
<html xmlns='http://jabber.org/protocol/xhtml-im'>
<body xmlns='http://www.w3.org/1999/xhtml'>
<p style='font-weight:bold'>Hello?</t>
</body>
</html>
</message>
<iq from='juliet@capulet.com/balcony'
id='roster2'
type='get'>
<query xmlns='jabber:iq:roster'>
<headers xmlns='http://jabber.org/protocol/shim'>
<header name='If-None-Match'>some-long-opaque-string</header>
</headers>
</query>
</iq>
An implementation SHOULD NOT generate namespace prefixes for elements
qualified by content (as opposed to stream) namespaces other than
'jabber:client' and 'jabber:server'. However, if included, the
namespace declarations for those prefixes MUST be included on the
stanza root or a child thereof, not at the level of the stream
element (this helps to ensure that any such namespace declaration is
routed and delivered with the stanza, instead of assumed from the
stream).
12.3. Validation
A server is not responsible for ensuring that XML data delivered to a
client or routed to another server is valid as the term "valid" is
defined in Section 2.8 of [XML]. An implementation MAY choose to
provide only validated data, but such behavior is OPTIONAL. A client
SHOULD NOT rely on the ability to send data that does not conform to
the schemas, and SHOULD ignore any non-conformant elements or
attributes on the incoming XML stream.
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Note: The terms "valid" and "well-formed" are distinct in XML. All
XMPP data MUST be well-formed as the term "well-formed" is defined in
Section 2.1 of [XML].
12.4. Inclusion of Text Declaration
Implementations SHOULD send a text declaration before sending a
stream header. Applications MUST follow the rules in [XML] regarding
the circumstances under which a text declaration is included.
12.5. Character Encoding
Implementations MUST support the [UTF-8] transformation of Universal
Character Set ([UCS2]) characters, as required by [CHARSET].
Implementations MUST NOT attempt to use any other encoding. If an
implementation detects that an entity has attempted to send XML data
with an encoding other than UTF-8, it MUST return a stream error,
which SHOULD be <unsupported-encoding/>.
12.6. White Space
Except where explicitly disallowed (i.e., during TLS negotiation
(Section 6) and SASL negotiation (Section 7)), either entity MAY send
white space characters (matching production [3] content of [XML])
within the root stream element as separators between XML stanzas or
between any other first-level elements sent over the stream; one
common use for sending such white space characters is to check the
viability of the underlying TCP connection after a period of
inactivity.
13. Compliance Requirements
This section summarizes the specific aspects of the Extensible
Messaging and Presence Protocol that MUST be supported by servers and
clients in order to be considered compliant implementations, as well
as additional protocol aspects that SHOULD be supported. For
compliance purposes, we draw a distinction between core protocols
(which MUST be supported by any server or client, regardless of the
specific application) and instant messaging and presence protocols
(which MUST be supported only by instant messaging and presence
applications built on top of the core protocols). Compliance
requirements that apply to all servers and clients are specified in
this section; compliance requirements for instant messaging and
presence applications are specified in the corresponding section of
[XMPP-IM].
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13.1. Servers
In addition to all defined requirements with regard to security, XML
usage, and internationalization, a server MUST support the following
core protocols in order to be considered compliant:
o Conformance with [IDNA] for domain identifiers, the Nodeprep
(Appendix A) profile of [STRINGPREP] for node identifiers, and the
Resourceprep (Appendix B) profile of [STRINGPREP] for resource
identifiers, as well as enforcement thereof for clients that
authenticate with the server.
o XML streams (Section 5), including TLS negotiation (Section 6),
SASL negotiation (Section 7), and Resource Binding (Section 8)
o The basic semantics of the three defined stanza types (i.e.,
<message/>, <presence/>, and <iq/>) as specified in stanza
semantics (Section 9.2)
o Generation (and, where appropriate, handling) of error syntax and
semantics related to streams, TLS, SASL, and XML stanzas
For backward compatibility with the large deployed base of XMPP
servers, server developers are advised to implement the server
dialback protocol first specified in [RFC3920] and now documented in
[XEP-0220], since that protocol is widely used for weak identity
verification of peer servers in the absence of domain certificates.
13.2. Clients
A client MUST support the following core protocols in order to be
considered compliant:
o XML streams (Section 5), including TLS negotiation (Section 6),
SASL negotiation (Section 7), and Resource Binding (Section 8)
o The basic semantics of the three defined stanza types (i.e.,
<message/>, <presence/>, and <iq/>) as specified in Section 9.2
o Handling (and, where appropriate, generation) of error syntax and
semantics related to streams, TLS, SASL, and XML stanzas
In addition, a client SHOULD support the following core protocols:
o Conformance with [IDNA] for domain identifiers, the Nodeprep
(Appendix A) profile of [STRINGPREP] for node identifiers, and the
Resourceprep (Appendix B) profile of [STRINGPREP] for resource
identifiers.
14. Internationalization Considerations
XML streams MUST be encoded in UTF-8 as specified under Section 12.5.
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As specified under Section 5.3, an XML stream SHOULD include an 'xml:
lang' attribute specifying the default language for any XML character
data sent over the stream that is intended to be presented to a human
user. As specified under Section 9.1.5, an XML stanza SHOULD include
an 'xml:lang' attribute if the stanza contains XML character data
that is intended to be presented to a human user. A server SHOULD
apply the default 'xml:lang' attribute to stanzas it routes or
delivers on behalf of connected entities, and MUST NOT modify or
delete 'xml:lang' attributes on stanzas it receives from other
entities.
15. Security Considerations
15.1. High Security
For the purposes of XMPP communication (client-to-server and server-
to-server), the term "high security" refers to the use of security
technologies that provide both mutual authentication and integrity-
checking; in particular, when using certificate-based authentication
to provide high security, a chain-of-trust SHOULD be established out-
of-band, although a shared certificate authority signing certificates
could allow a previously unknown certificate to establish trust in-
band. See Section 15.2 regarding certificate validation procedures.
Implementations MUST support high security. Service provisioning
should use high security, subject to local security policies.
15.2. Certificate Validation
When an XMPP peer communicates with another peer securely, it MUST
validate the peer's certificate. There are three possible cases:
Case #1: The peer contains an End Entity certificate that appears to
be certified by a chain of certificates terminating in a trust
anchor (as described in Section 6.1 of [X509]).
Case #2: The peer certificate is certified by a Certificate
Authority not known to the validating peer.
Case #3: The peer certificate is self-signed.
In Case #1, the validating peer MUST do one of two things:
1. Verify the peer certificate according to the rules of [X509].
The certificate SHOULD then be checked against the expected
identity of the peer following the rules described in [HTTP-TLS],
except that if present an [ASN.1] Object Identifier of "id-on-
xmppAddr" (represented as a UTF8String in an otherName entity
inside the subjectAltName) MUST be used as the identity. If one
of these checks fails, user-oriented clients MUST either notify
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the user (clients MAY give the user the opportunity to continue
with the connection anyway) or terminate the connection with a
bad certificate error. Automated clients SHOULD terminate the
connection (with a bad certificate error) and log the error to an
appropriate audit log. Automated clients MAY provide a
configuration setting that disables this check, but MUST provide
a setting that enables it.
2. The peer SHOULD show the certificate to a user for approval,
including the entire certificate chain. The peer MUST cache the
certificate (or some non-forgeable representation such as a
hash). In future connections, the peer MUST verify that the same
certificate was presented and MUST notify the user if it has
changed.
In Case #2 and Case #3, implementations SHOULD act as in Rule #2 for
Case #1.
15.3. Client-to-Server Communication
A compliant client implementation MUST support both TLS and SASL for
connections to a server.
The TLS protocol for encrypting XML streams (defined under Section 6)
provides a reliable mechanism for helping to ensure the
confidentiality and data integrity of data exchanged between two
entities.
The SASL protocol for authenticating XML streams (defined under
Section 7) provides a reliable mechanism for validating that a client
connecting to a server is who it claims to be.
Client-to-server communication MUST NOT proceed until the DNS
hostname asserted by the server has been resolved as specified under
Section 4. If there is a mismatch between the hostname to which a
client attempted to connect (e.g., "example.net") and the hostname to
which the client actually connects (e.g., "xmpp.example.net"), the
client MUST warn a human user about the mismatch and the human user
MUST approve the connection before the client proceeds; however, the
client MAY also allow the user to add the presented hostname to a
configured set of accepted hostnames in order to expedite future
connections.
The IP address and method of access of clients MUST NOT be made
public by a server, nor are any connections other than the original
server connection required. This helps to protect the client's
server from direct attack or identification by third parties.
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15.4. Server-to-Server Communication
A compliant server implementation MUST support both TLS and SASL for
inter-domain communication.
Because service provisioning is a matter of policy, it is optional
for any given domain to communicate with other domains, and server-
to-server communication may be disabled by the administrator of any
given deployment. If a particular domain enables inter-domain
communication, it should enable high security.
Administrators may want to require use of SASL for server-to-server
communication in order to ensure both authentication and
confidentiality (e.g., on an organization's private network).
Compliant implementations SHOULD support SASL for this purpose.
Server-to-server communication MUST NOT proceed until the DNS
hostnames asserted by both servers have been resolved as specified
under Section 4.
15.5. Order of Layers
The order of layers in which protocols MUST be stacked is:
1. TCP
2. TLS
3. SASL
4. XMPP
The rationale for this order is that [TCP] is the base connection
layer used by all of the protocols stacked on top of TCP, [TLS] is
often provided at the operating system layer, [SASL] is often
provided at the application layer, and XMPP is the application
itself.
15.6. Lack of SASL Channel Binding to TLS
The SASL framework does not provide a mechanism to bind SASL
authentication to a security layer providing confidentiality and
integrity protection that was negotiated at a lower layer. This lack
of a "channel binding" prevents SASL from being able to verify that
the source and destination end points to which the lower layer's
security is bound are equivalent to the end points that SASL is
authenticating. If the end points are not identical, the lower
layer's security cannot be trusted to protect data transmitted
between the SASL authenticated entities. In such a situation, a SASL
security layer SHOULD be negotiated that effectively ignores the
presence of the lower layer security.
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15.7. Mandatory-to-Implement Technologies
At a minimum, all implementations MUST support the following
mechanisms:
for authentication: the SASL [DIGEST-MD5] mechanism
for confidentiality: TLS (using the TLS_RSA_WITH_3DES_EDE_CBC_SHA
cipher)
for both: TLS plus SASL PLAIN for client-to-server connections and
TLS plus SASL EXTERNAL for server-to-server connections (using the
TLS_RSA_WITH_3DES_EDE_CBC_SHA cipher supporting peer certificates)
Naturally, implementations MAY support other ciphers with TLS and MAY
support other SASL mechanisms.
15.8. Firewalls
Communication using XMPP normally occurs over [TCP] connections on
port 5222 (client-to-server) or port 5269 (server-to-server), as
registered with the IANA (see Section 16). Use of these well-known
ports allows administrators to easily enable or disable XMPP activity
through existing and commonly-deployed firewalls.
15.9. Use of base64 in SASL
Both the client and the server MUST verify any [BASE64] data received
during SASL negotiation (Section 7). An implementation MUST reject
(not ignore) any characters that are not explicitly allowed by the
base64 alphabet; this helps to guard against creation of a covert
channel that could be used to "leak" information. An implementation
MUST NOT break on invalid input and MUST reject any sequence of
base64 characters containing the pad ('=') character if that
character is included as something other than the last character of
the data (e.g., "=AAA" or "BBBB=CCC"); this helps to guard against
buffer overflow attacks and other attacks on the implementation.
Base 64 encoding visually hides otherwise easily recognized
information, such as passwords, but does not provide any
computational confidentiality. Base 64 encoding MUST follow the
definition in Section 4 of [BASE64] and padding bits MUST be set to
zero.
15.10. Stringprep Profiles
XMPP makes use of the [NAMEPREP] profile of [STRINGPREP] for
processing of domain identifiers; for security considerations related
to Nameprep, refer to the appropriate section of [NAMEPREP].
In addition, XMPP defines two profiles of [STRINGPREP]: Nodeprep
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(Appendix A) for node identifiers and Resourceprep (Appendix B) for
resource identifiers.
The Unicode and ISO/IEC 10646 repertoires have many characters that
look similar. In many cases, users of security protocols might do
visual matching, such as when comparing the names of trusted third
parties. Because it is impossible to map similar-looking characters
without a great deal of context, such as knowing the fonts used,
stringprep does nothing to map similar-looking characters together,
nor to prohibit some characters because they look like others.
A node identifier can be employed as one part of an entity's address
in XMPP. One common usage is as the username of an instant messaging
user; another is as the name of a multi-user conference room; many
other kinds of entities could use node identifiers as part of their
addresses. The security of such services could be compromised based
on different interpretations of the internationalized node
identifier; for example, a user entering a single internationalized
node identifier could access another user's account information, or a
user could gain access to a hidden or otherwise restricted chat room
or service.
A resource identifier can be employed as one part of an entity's
address in XMPP. One common usage is as the name for an instant
messaging user's connected resource; another is as the nickname of a
user in a multi-user conference room; many other kinds of entities
could use resource identifiers as part of their addresses. The
security of such services could be compromised based on different
interpretations of the internationalized resource identifier; for
example, a user could attempt to initiate multiple connections with
the same name, or a user could send a message to someone other than
the intended recipient in a multi-user conference room.
15.11. Address Spoofing
As discussed in [XEP-0165], there are two forms of address spoofing:
forging and mimicking.
15.11.1. Address Forging
In the context of XMPP technologies, address forging occurs when an
entity is able to generate an XML stanza whose 'from' address does
not correspond to the account credentials with which the entity
authenticated onto the network (or an authorization identity provided
during SASL negotiation (Section 7). For example, address forging
occurs if an entity that authenticated as "juliet@example.com" is
able to send XML stanzas from "nurse@example.com" or
"romeo@example.net".
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Address forging is difficult in XMPP systems, given the requirement
for sending servers to stamp 'from' addresses and for receiving
servers to verify sending domains via server-to-server
authentication. However, address forging is not impossible, since a
rogue server could forge JIDs at the sending domain by ignoring the
stamping requirement. A rogue server could even forge JIDs at other
domains by means of a DNS poisoning attack if [DNSSEC] is not used.
This specification does not define methods for discovering or
counteracting such rogue servers.
15.11.2. Address Mimicking
Address mimicking occus when an entity provides legitimate
authentication credentials for and sends XML stanzas from an account
whose JID appears to a human user to be the same as another JID. For
example, in some XMPP clients the address "paypa1@example.org"
(spelled with the number one as the final character of the node
identifier) may appear to be the same as "paypal@example.org (spelled
with the lower-case version of the letter "L"), especially on casual
visual inspection; this phenomenon is sometimes called "typejacking".
A more sophisticated example of address mimicking might involve the
use of characters from outside the US-ASCII range, such as the
Cherokee characters U+13DA U+13A2 U+13B5 U+13AC U+13A2 U+13AC U+13D2
instead of the US-ASCII characters "STPETER".
In some examples of address mimicking, it is unlikely that the
average user could tell the difference between the real JID and the
fake JID. (Naturally, there is no way to distinguish with full
certainty which is the fake JID and which is the real JID; in some
communication contexts, the JID with Cherokee characters may be the
real JID and the JID with US-ASCII characters may thus appear to be
the fake JID.) Because JIDs can contain almost any Unicode
character, it may be relatively easy to mimic some JIDs in XMPP
systems. The possibility of address mimicking introduces security
vulnerabilities of the kind that have also plagued the World Wide
Web, specifically the phenomenon known as phishing.
Mimicked addresses that involve characters from only one character
set or from the character set typically employed by a particular user
are not easy to combat (e.g., the simple typejacking attack
previously described, which relies on a surface similarity between
the characters "1" and "l" in some presentations). However, mimicked
addresses that involve characters from more than one character set,
or from a character set not typically employed by a particular user,
can be mitigated somewhat through intelligent presentation. In
particular, every human user of an XMPP technology presumably has a
preferred language (or, in some cases, a small set of preferred
languages), which an XMPP application SHOULD gather either explicitly
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from the user or implicitly via the operating system of the user's
device. Furthermore, every language has a range (or a small set of
ranges) of characters normally used to represent that language in
textual form. Therefore, an XMPP application SHOULD warn the user
when presenting a JID that uses characters outside the normal range
of the user's preferred language(s). This recommendation is not
intended to discourage communication across language communities;
instead, it recognizes the existence of such language communities and
encourages due caution when presenting unfamiliar character sets to
human users.
For more detailed recommendations regarding prevention of address
mimicking in XMPP systems, refer to [XEP-0165].
15.12. Denial of Service
[DOS] defines denial of service as follows:
A Denial-of-Service (DoS) attack is an attack in which one or more
machines target a victim and attempt to prevent the victim from
doing useful work. The victim can be a network server, client or
router, a network link or an entire network, an individual
Internet user or a company doing business using the Internet, an
Internet Service Provider (ISP), country, or any combination of or
variant on these.
[XEP-0205] provides a detailed discussion of potential denial of
service attacks against XMPP systems and best practices for
preventing such attacks. The recommendations include:
1. A server implementation SHOULD enable a server administrator to
limit the number of TCP connections that it will accept from a
given IP address at any one time. If an entity attempts to
connect but the maximum number of TCP connections has been
reached, the receiving server MUST NOT allow the new connection
to proceed.
2. A server implementation SHOULD enable a server administrator to
limit the number of TCP connection attempts that it will accept
from a given IP address in a given time period. (While it is
possible to limit the number of connections at the TCP layer
rather than at the XMPP application layer, care must be taken in
doing so since limits at the TCP layer might result in an
inability to access non-XMPP services.) If an entity attempts to
connect but the maximum number of connections has been reached,
the receiving server MUST NOT allow the new connection to
proceed.
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3. A server MUST NOT process XML stanzas from clients that have not
yet provided appropriate authentication credentials and MUST NOT
process XML stanzas from peer servers whose identity it has not
either authenticated via SASL.
4. A server implementation SHOULD enable a server administrator to
limit the number of connected resources it will allow an account
to bind at any one time. If a client attempts to bind a resource
but it has already reached the configured number of allowable
resources, the receiving server MUST return a <not-allowed>
stanza error.
5. A server implementation SHOULD enable a server administrator to
limit the size of stanzas it will accept from a connected client
or peer server. If a connected resource or peer server sends a
stanza that violates the upper limit, the receiving server SHOULD
NOT process the stanza and instead SHOULD return a <not-allowed>
stanza error. Alternatively (e.g., if the sender has sent an
egregiously large stanza), the server MAY instead return a
<policy-violation/> stream error.
6. A server implementation SHOULD enable a server administrator to
limit the number of XML stanzas that a connected client may send
to distinct recipients within a given time period. If a
connected client sends too many stanzas to distinct recipients in
a given time period, the receiving server SHOULD NOT process the
stanza and instead SHOULD return an <unexpected-request> stanza
error.
7. A server implementation SHOULD enable a server administrator to
limit the amount of bandwidth it will allow a connected client or
peer server to use in a given time period.
8. A server implementation SHOULD enable a server administrator to
limit the types of stanzas (based on the extended content
"payload") that it will allow a connected resource or peer server
send over an active connection. Such limits and restrictions are
a matter of deployment policy.
For more detailed recommendations regarding denial of service attacks
in XMPP systems, refer to [XEP-0205].
15.13. Presence Leaks
One of the core aspects of XMPP is presence, i.e., ubiquitous
information about the network availability of XMPP entities.
Although presence is discussed more fully in [XMPP-IM], it is
important to note that an XMPP server MUST NOT disclose an entity's
presence to entities that are not authorized to know that information
(such a disclosure is called a "presence leak"). In particular at
the core XMPP level, real-time addressing and network availability is
associated with a specific connected resource; therefore, any
disclosure of a connected resource's full JID comprises a presence
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leak. To help prevent such a presence leak, a server MUST NOT return
different stanza errors if a potential attacker sends XML stanzas to
the entity's bare JID (<node@domain>) or full JID
(<node@domain/resource>).
15.14. Directory Harvesting
To help prevent directory harvesting attacks, server MUST NOT return
different stanza errors if a potential attacker sends XML stanzas to
an existing entity or a nonexistent entity. The stanza error
returned in both cases SHOULD be <service-unavailable/>.
16. IANA Considerations
The following sections update the registrations provided in
[RFC3920].
16.1. XML Namespace Name for TLS Data
A URN sub-namespace for TLS-related data in the Extensible Messaging
and Presence Protocol (XMPP) is defined as follows. (This namespace
name adheres to the format defined in [XML-REG].)
URI: urn:ietf:params:xml:ns:xmpp-tls
Specification: XXXX
Description: This is the XML namespace name for TLS-related data in
the Extensible Messaging and Presence Protocol (XMPP) as defined
by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@xmpp.org>
16.2. XML Namespace Name for SASL Data
A URN sub-namespace for SASL-related data in the Extensible Messaging
and Presence Protocol (XMPP) is defined as follows. (This namespace
name adheres to the format defined in [XML-REG].)
URI: urn:ietf:params:xml:ns:xmpp-sasl
Specification: XXXX
Description: This is the XML namespace name for SASL-related data in
the Extensible Messaging and Presence Protocol (XMPP) as defined
by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@xmpp.org>
16.3. XML Namespace Name for Stream Errors
A URN sub-namespace for stream-related error data in the Extensible
Messaging and Presence Protocol (XMPP) is defined as follows. (This
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namespace name adheres to the format defined in [XML-REG].)
URI: urn:ietf:params:xml:ns:xmpp-streams
Specification: XXXX
Description: This is the XML namespace name for stream-related error
data in the Extensible Messaging and Presence Protocol (XMPP) as
defined by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@xmpp.org>
16.4. XML Namespace Name for Resource Binding
A URN sub-namespace for resource binding in the Extensible Messaging
and Presence Protocol (XMPP) is defined as follows. (This namespace
name adheres to the format defined in [XML-REG].)
URI: urn:ietf:params:xml:ns:xmpp-bind
Specification: XXXX
Description: This is the XML namespace name for resource binding in
the Extensible Messaging and Presence Protocol (XMPP) as defined
by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@xmpp.org>
16.5. XML Namespace Name for Stanza Errors
A URN sub-namespace for stanza-related error data in the Extensible
Messaging and Presence Protocol (XMPP) is defined as follows. (This
namespace name adheres to the format defined in [XML-REG].)
URI: urn:ietf:params:xml:ns:xmpp-stanzas
Specification: XXXX
Description: This is the XML namespace name for stanza-related error
data in the Extensible Messaging and Presence Protocol (XMPP) as
defined by XXXX.
Registrant Contact: IETF, XMPP Working Group, <xmppwg@xmpp.org>
16.6. Nodeprep Profile of Stringprep
The Nodeprep profile of stringprep is defined under Nodeprep
(Appendix A). The IANA has registered Nodeprep in the stringprep
profile registry.
Name of this profile:
Nodeprep
RFC in which the profile is defined:
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XXXX
Indicator whether or not this is the newest version of the profile:
This is the first version of Nodeprep
16.7. Resourceprep Profile of Stringprep
The Resourceprep profile of stringprep is defined under Resourceprep
(Appendix B). The IANA has registered Resourceprep in the stringprep
profile registry.
Name of this profile:
Resourceprep
RFC in which the profile is defined:
XXXX
Indicator whether or not this is the newest version of the profile:
This is the first version of Resourceprep
16.8. GSSAPI Service Name
The IANA has registered "xmpp" as a GSSAPI [GSS-API] service name, as
defined under Section 7.4.
16.9. Port Numbers
The IANA has registered "xmpp-client" and "xmpp-server" as keywords
for [TCP] ports 5222 and 5269 respectively.
These ports SHOULD be used for client-to-server and server-to-server
communications respectively, but their use is OPTIONAL.
17. References
17.1. Normative References
[ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
[BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
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[CHARSET] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998.
[DIGEST-MD5]
Leach, P. and C. Newman, "Using Digest Authentication as a
SASL Mechanism", RFC 2831, May 2000.
[DNS-SRV] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[DNS] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[IDNA] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003.
[IPv6] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[LANGTAGS]
Phillips, A. and M. Davis, "Tags for Identifying
Languages", BCP 47, RFC 4646, September 2006.
[NAMEPREP]
Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
Profile for Internationalized Domain Names (IDN)",
RFC 3491, March 2003.
[RANDOM] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 2005.
[SASL] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
[STRINGPREP]
Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings ("stringprep")", RFC 3454,
December 2002.
[TCP] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[TERMS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[TLS] Dierks, T. and E. Rescorla, "The Transport Layer Security
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(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[UCS2] International Organization for Standardization,
"Information Technology - Universal Multiple-octet coded
Character Set (UCS) - Amendment 2: UCS Transformation
Format 8 (UTF-8)", ISO Standard 10646-1 Addendum 2,
October 1996.
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[UUID] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
July 2005.
[X509] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[XML] Paoli, J., Maler, E., Sperberg-McQueen, C., Yergeau, F.,
and T. Bray, "Extensible Markup Language (XML) 1.0 (Fourth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20060816, August 2006,
<http://www.w3.org/TR/2006/REC-xml-20060816>.
[XML-NAMES]
Bray, T., Hollander, D., and A. Layman, "Namespaces in
XML", W3C REC-xml-names, January 1999,
<http://www.w3.org/TR/REC-xml-names>.
17.2. Informative References
[ACAP] Newman, C. and J. Myers, "ACAP -- Application
Configuration Access Protocol", RFC 2244, November 1997.
[ASN.1] CCITT, "Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1)", 1988.
[DNSSEC] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, March 2005.
[DNS-TXT] Rosenbaum, R., "Using the Domain Name System To Store
Arbitrary String Attributes", RFC 1464, May 1993.
[DOS] Handley, M., Rescorla, E., and IAB, "Internet Denial-of-
Service Considerations", RFC 4732, December 2006.
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[GSS-API] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[HTTP] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[HTTP-TLS]
Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[IMAP] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.
[IMP-REQS]
Day, M., Aggarwal, S., and J. Vincent, "Instant Messaging
/ Presence Protocol Requirements", RFC 2779,
February 2000.
[IRI] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[LINKLOCAL]
Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927,
May 2005.
[MAILBOXES]
Crocker, D., "MAILBOX NAMES FOR COMMON SERVICES, ROLES AND
FUNCTIONS", RFC 2142, May 1997.
[POP3] Myers, J. and M. Rose, "Post Office Protocol - Version 3",
STD 53, RFC 1939, May 1996.
[PUNYCODE]
Costello, A., "Punycode: A Bootstring encoding of Unicode
for Internationalized Domain Names in Applications
(IDNA)", RFC 3492, March 2003.
[RFC3920] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004.
[SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
April 2001.
[STD13] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
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Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[URN-OID] Mealling, M., "A URN Namespace of Object Identifiers",
RFC 3061, February 2001.
[USINGTLS]
Newman, C., "Using TLS with IMAP, POP3 and ACAP",
RFC 2595, June 1999.
[XEP-0045]
Saint-Andre, P., "Multi-User Chat", XSF XEP 0045,
April 2007.
[XEP-0060]
Millard, P., Saint-Andre, P., and R. Meijer, "Publish-
Subscribe", XSF XEP 0060, September 2006.
[XEP-0071]
Saint-Andre, P., "XHTML-IM", XSF XEP 0071, March 2007.
[XEP-0077]
Saint-Andre, P., "In-Band Registration", XSF XEP 0077,
January 2006.
[XEP-0086]
Norris, R. and P. Saint-Andre, "Error Condition Mappings",
XSF XEP 0086, February 2004.
[XEP-0124]
Paterson, I., Smith, D., and P. Saint-Andre,
"Bidirectional-streams Over Synchronous HTTP (BOSH)", XSF
XEP 0124, February 2007.
[XEP-0156]
Hildebrand, J. and P. Saint-Andre, "Discovering
Alternative XMPP Connection Methods", XSF XEP 0156,
January 2007.
[XEP-0157]
Saint-Andre, P. and J. Konieczny, "Contact Addresses for
XMPP Services", XSF XEP 0157, January 2007.
[XEP-0165]
Saint-Andre, P., "Best Practices to Prevent JID
Mimicking", XSF XEP 0165, December 2006.
[XEP-0174]
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Saint-Andre, P., "Link-Local Messaging", XSF XEP 0174,
March 2007.
[XEP-0175]
Saint-Andre, P., "Best Practices for Use of SASL
ANONYMOUS", XSF XEP 0175, September 2006.
[XEP-0178]
Saint-Andre, P. and P. Millard, "Best Practices for Use of
SASL EXTERNAL with Certificates", XSF XEP 0178,
February 2007.
[XEP-0205]
Saint-Andre, P., "Best Practices to Discourage Denial of
Service Attacks", XSF XEP 0205, January 2007.
[XEP-0206]
Paterson, I., "XMPP Over BOSH", XSF XEP 0206,
February 2007.
[XEP-0220]
Saint-Andre, P. and J. Miller, "Server Dialback", XSF
XEP 0220, June 2007.
[XML-REG] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[XML-SCHEMA]
Thompson, H., Maloney, M., Mendelsohn, N., and D. Beech,
"XML Schema Part 1: Structures Second Edition", World Wide
Web Consortium Recommendation REC-xmlschema-1-20041028,
October 2004,
<http://www.w3.org/TR/2004/REC-xmlschema-1-20041028>.
[XMPP-IM] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
draft-saintandre-rfc3921bis-03 (work in progress),
July 2007.
[XMPP-URI]
Saint-Andre, P., "Internationalized Resource Identifiers
(IRIs) and Uniform Resource Identifiers (URIs) for the
Extensible Messaging and Presence Protocol (XMPP)",
draft-saintandre-rfc4622bis-01 (work in progress),
June 2007.
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Appendix A. Nodeprep
A.1. Introduction
This appendix defines the "Nodeprep" profile of [STRINGPREP]. As
such, it specifies processing rules that will enable users to enter
internationalized node identifiers in the Extensible Messaging and
Presence Protocol (XMPP) and have the highest chance of getting the
content of the strings correct. (An XMPP node identifier is the
optional portion of an XMPP address that precedes an XMPP domain
identifier and the '@' separator; it is often but not exclusively
associated with an instant messaging username.) These processing
rules are intended only for XMPP node identifiers and are not
intended for arbitrary text or any other aspect of an XMPP address.
This profile defines the following, as required by [STRINGPREP]:
o The intended applicability of the profile: internationalized node
identifiers within XMPP
o The character repertoire that is the input and output to
stringprep: Unicode 3.2, specified in Section 2 of this Appendix
o The mappings used: specified in Section 3
o The Unicode normalization used: specified in Section 4
o The characters that are prohibited as output: specified in Section
5
o Bidirectional character handling: specified in Section 6
A.2. Character Repertoire
This profile uses Unicode 3.2 with the list of unassigned code points
being Table A.1, both defined in Appendix A of [STRINGPREP].
A.3. Mapping
This profile specifies mapping using the following tables from
[STRINGPREP]:
Table B.1
Table B.2
A.4. Normalization
This profile specifies the use of Unicode normalization form KC, as
described in [STRINGPREP].
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A.5. Prohibited Output
This profile specifies the prohibition of using the following tables
from [STRINGPREP].
Table C.1.1
Table C.1.2
Table C.2.1
Table C.2.2
Table C.3
Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
In addition, the following Unicode characters are also prohibited:
#x22 (")
#x26 (&)
#x27 (')
#x2F (/)
#x3A (:)
#x3C (<)
#x3E (>)
#x40 (@)
A.6. Bidirectional Characters
This profile specifies checking bidirectional strings, as described
in Section 6 of [STRINGPREP].
Appendix B. Resourceprep
B.1. Introduction
This appendix defines the "Resourceprep" profile of [STRINGPREP]. As
such, it specifies processing rules that will enable users to enter
internationalized resource identifiers in the Extensible Messaging
and Presence Protocol (XMPP) and have the highest chance of getting
the content of the strings correct. (An XMPP resource identifier is
the optional portion of an XMPP address that follows an XMPP domain
identifier and the '/' separator.) These processing rules are
intended only for XMPP resource identifiers and are not intended for
arbitrary text or any other aspect of an XMPP address.
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This profile defines the following, as required by [STRINGPREP]:
o The intended applicability of the profile: internationalized
resource identifiers within XMPP
o The character repertoire that is the input and output to
stringprep: Unicode 3.2, specified in Section 2 of this Appendix
o The mappings used: specified in Section 3
o The Unicode normalization used: specified in Section 4
o The characters that are prohibited as output: specified in Section
5
o Bidirectional character handling: specified in Section 6
B.2. Character Repertoire
This profile uses Unicode 3.2 with the list of unassigned code points
being Table A.1, both defined in Appendix A of [STRINGPREP].
B.3. Mapping
This profile specifies mapping using the following tables from
[STRINGPREP]:
Table B.1
B.4. Normalization
This profile specifies the use of Unicode normalization form KC, as
described in [STRINGPREP].
B.5. Prohibited Output
This profile specifies the prohibition of using the following tables
from [STRINGPREP].
Table C.1.2
Table C.2.1
Table C.2.2
Table C.3
Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
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B.6. Bidirectional Characters
This profile specifies checking bidirectional strings, as described
in Section 6 of [STRINGPREP].
Appendix C. XML Schemas
Because validation of XML streams and stanzas is optional, the
following XML schemas are provided for descriptive purposes only.
These schemas are not normative.
The following schemas formally define various XML namespaces used in
the core XMPP protocols, in conformance with [XML-SCHEMA]. For
schemas defining the 'jabber:client' and 'jabber:server' namespaces,
refer to [XMPP-IM].
C.1. Streams namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='http://etherx.jabber.org/streams'
xmlns='http://etherx.jabber.org/streams'
elementFormDefault='unqualified'>
<xs:import namespace='jabber:client'/>
<xs:import namespace='jabber:server'/>
<xs:element name='stream'>
<xs:complexType>
<xs:sequence xmlns:client='jabber:client'
xmlns:server='jabber:server'>
<xs:element ref='features' minOccurs='0' maxOccurs='1'/>
<xs:any namespace='urn:ietf:params:xml:ns:xmpp-tls'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:any namespace='urn:ietf:params:xml:ns:xmpp-sasl'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:choice minOccurs='0' maxOccurs='1'>
<xs:choice minOccurs='0' maxOccurs='unbounded'>
<xs:element ref='client:message'/>
<xs:element ref='client:presence'/>
<xs:element ref='client:iq'/>
</xs:choice>
<xs:choice minOccurs='0' maxOccurs='unbounded'>
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<xs:element ref='server:message'/>
<xs:element ref='server:presence'/>
<xs:element ref='server:iq'/>
<xs:element ref='db:result'/>
<xs:element ref='db:verify'/>
</xs:choice>
</xs:choice>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='from' type='xs:string' use='optional'/>
<xs:attribute name='id' type='xs:string' use='optional'/>
<xs:attribute name='to' type='xs:string' use='optional'/>
<xs:attribute name='version' type='xs:decimal' use='optional'/>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='features'>
<xs:complexType>
<xs:any namespace='##other'/>
</xs:complexType>
</xs:element>
<xs:element name='error'>
<xs:complexType>
<xs:sequence xmlns:err='urn:ietf:params:xml:ns:xmpp-streams'>
<xs:group ref='err:streamErrorGroup'/>
<xs:element ref='err:text'
minOccurs='0'
maxOccurs='1'/>
<xs:any namespace='##other'
minOccurs='0'
maxOccurs='1'/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
C.2. Stream error namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-streams'
xmlns='urn:ietf:params:xml:ns:xmpp-streams'
elementFormDefault='qualified'>
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<xs:element name='bad-format' type='empty'/>
<xs:element name='bad-namespace-prefix' type='empty'/>
<xs:element name='conflict' type='empty'/>
<xs:element name='connection-timeout' type='empty'/>
<xs:element name='host-gone' type='empty'/>
<xs:element name='host-unknown' type='empty'/>
<xs:element name='improper-addressing' type='empty'/>
<xs:element name='internal-server-error' type='empty'/>
<xs:element name='invalid-from' type='empty'/>
<xs:element name='invalid-id' type='empty'/>
<xs:element name='invalid-namespace' type='empty'/>
<xs:element name='invalid-xml' type='empty'/>
<xs:element name='not-authorized' type='empty'/>
<xs:element name='policy-violation' type='empty'/>
<xs:element name='remote-connection-failed' type='empty'/>
<xs:element name='resource-constraint' type='empty'/>
<xs:element name='restricted-xml' type='empty'/>
<xs:element name='see-other-host' type='xs:string'/>
<xs:element name='system-shutdown' type='empty'/>
<xs:element name='undefined-condition' type='empty'/>
<xs:element name='unsupported-encoding' type='empty'/>
<xs:element name='unsupported-stanza-type' type='empty'/>
<xs:element name='unsupported-version' type='empty'/>
<xs:element name='xml-not-well-formed' type='empty'/>
<xs:group name='streamErrorGroup'>
<xs:choice>
<xs:element ref='bad-format'/>
<xs:element ref='bad-namespace-prefix'/>
<xs:element ref='conflict'/>
<xs:element ref='connection-timeout'/>
<xs:element ref='host-gone'/>
<xs:element ref='host-unknown'/>
<xs:element ref='improper-addressing'/>
<xs:element ref='internal-server-error'/>
<xs:element ref='invalid-from'/>
<xs:element ref='invalid-id'/>
<xs:element ref='invalid-namespace'/>
<xs:element ref='invalid-xml'/>
<xs:element ref='not-authorized'/>
<xs:element ref='policy-violation'/>
<xs:element ref='remote-connection-failed'/>
<xs:element ref='resource-constraint'/>
<xs:element ref='restricted-xml'/>
<xs:element ref='see-other-host'/>
<xs:element ref='system-shutdown'/>
<xs:element ref='undefined-condition'/>
<xs:element ref='unsupported-encoding'/>
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<xs:element ref='unsupported-stanza-type'/>
<xs:element ref='unsupported-version'/>
<xs:element ref='xml-not-well-formed'/>
</xs:choice>
</xs:group>
<xs:element name='text'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
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C.3. TLS namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-tls'
xmlns='urn:ietf:params:xml:ns:xmpp-tls'
elementFormDefault='qualified'>
<xs:element name='starttls'>
<xs:complexType>
<xs:sequence>
<xs:element name='required'
minOccurs='0'
type='empty'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='proceed' type='empty'/>
<xs:element name='failure' type='empty'/>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
C.4. SASL namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-sasl'
xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
elementFormDefault='qualified'>
<xs:element name='mechanisms'>
<xs:complexType>
<xs:sequence>
<xs:element name='mechanism'
minOccurs='0'
maxOccurs='unbounded'
type='xs:NMTOKEN'/>
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<xs:element name='required'
minOccurs='0'
maxOccurs='1'
type='empty'/>
<xs:any namespace='##other'
minOccurs='0'
minOccurs='unbounded'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='auth'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute name='mechanism'
type='xs:NMTOKEN'
use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='abort' type='empty'/>
<xs:element name='challenge' type='xs:string'/>
<xs:element name='response' type='xs:string'/>
<xs:element name='success' type='xs:string'/>
<xs:element name='failure'>
<xs:complexType>
<xs:choice minOccurs='0'>
<xs:element name='aborted' type='empty'/>
<xs:element name='incorrect-encoding' type='empty'/>
<xs:element name='invalid-authzid' type='empty'/>
<xs:element name='invalid-mechanism' type='empty'/>
<xs:element name='malformed-request' type='empty'/>
<xs:element name='mechanism-too-weak' type='empty'/>
<xs:element name='not-authorized' type='empty'/>
<xs:element name='temporary-auth-failure' type='empty'/>
</xs:choice>
</xs:complexType>
</xs:element>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
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</xs:schema>
C.5. Resource binding namespace
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<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-bind'
xmlns='urn:ietf:params:xml:ns:xmpp-bind'
elementFormDefault='qualified'>
<xs:element name='bind'>
<xs:complexType>
<xs:sequence>
<xs:choice minOccurs='0' maxOccurs='1'>
<xs:element name='resource' type='resourceType'/>
<xs:element name='jid' type='fullJIDType'/>
</xs:choice>
<xs:element name='required'
minOccurs='0'
maxOccurs='1'
type='empty'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='unbind'>
<xs:complexType>
<xs:sequence minOccurs='0'>
<xs:element name='resource' type='resourceType'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:simpleType name='resourceType'>
<xs:restriction base='xs:string'>
<xs:minLength value='1'/>
<xs:maxLength value='1023'/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name='fullJIDType'>
<xs:restriction base='xs:string'>
<xs:minLength value='8'/>
<xs:maxLength value='3071'/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
C.6. Stanza error namespace
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<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-stanzas'
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'
elementFormDefault='qualified'>
<xs:element name='bad-request' type='empty'/>
<xs:element name='conflict' type='empty'/>
<xs:element name='feature-not-implemented' type='empty'/>
<xs:element name='forbidden' type='empty'/>
<xs:element name='gone' type='xs:string'/>
<xs:element name='internal-server-error' type='empty'/>
<xs:element name='item-not-found' type='empty'/>
<xs:element name='jid-malformed' type='empty'/>
<xs:element name='not-acceptable' type='empty'/>
<xs:element name='not-allowed' type='empty'/>
<xs:element name='not-modified' type='empty'/>
<xs:element name='payment-required' type='empty'/>
<xs:element name='recipient-unavailable' type='empty'/>
<xs:element name='redirect' type='xs:string'/>
<xs:element name='registration-required' type='empty'/>
<xs:element name='remote-server-not-found' type='empty'/>
<xs:element name='remote-server-timeout' type='empty'/>
<xs:element name='resource-constraint' type='empty'/>
<xs:element name='service-unavailable' type='empty'/>
<xs:element name='subscription-required' type='empty'/>
<xs:element name='undefined-condition' type='empty'/>
<xs:element name='unexpected-request' type='empty'/>
<xs:element name='unknown-sender' type='empty'/>
<xs:group name='stanzaErrorGroup'>
<xs:choice>
<xs:element ref='bad-request'/>
<xs:element ref='conflict'/>
<xs:element ref='feature-not-implemented'/>
<xs:element ref='forbidden'/>
<xs:element ref='gone'/>
<xs:element ref='internal-server-error'/>
<xs:element ref='item-not-found'/>
<xs:element ref='jid-malformed'/>
<xs:element ref='not-acceptable'/>
<xs:element ref='not-allowed'/>
<xs:element ref='not-modified'/>
<xs:element ref='payment-required'/>
<xs:element ref='recipient-unavailable'/>
<xs:element ref='redirect'/>
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<xs:element ref='registration-required'/>
<xs:element ref='remote-server-not-found'/>
<xs:element ref='remote-server-timeout'/>
<xs:element ref='resource-constraint'/>
<xs:element ref='service-unavailable'/>
<xs:element ref='subscription-required'/>
<xs:element ref='undefined-condition'/>
<xs:element ref='unexpected-request'/>
<xs:element ref='unknown-sender'/>
</xs:choice>
</xs:group>
<xs:element name='text'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute ref='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
Appendix D. Contact Addresses
Consistent with [MAILBOXES], an organization that offers an XMPP
service should provide an Internet mailbox of "XMPP" for inquiries
related to that service, where the host portion of the resulting
mailto URI should be the organization's domain, not necessarily the
domain of the XMPP service itself (e.g., the XMPP service might be
offered at xmpp.example.net but the Internet mailbox should be
<xmpp@example.net>).
In addition, the XMPP service should provide a way to discover the
XMPP contact address(es) of the service administrator(s), as
specified in [XEP-0157].
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Appendix E. Account Provisioning
Account provisioning is out of scope for this specification.
Possible methods for account provisioning include account creation by
a server administrator and in-band account registration using the
'jabber:iq:register' namespace as documented in [XEP-0077].
Appendix F. Differences From RFC 3920
Based on consensus derived from implementation and deployment
experience as well as formal interoperability testing, the following
substantive modifications were made from RFC 3920.
o Corrected the ABNF syntax for JIDs to prevent zero-length node
identifiers, domain identifiers, and resource identifiers.
o Corrected the nameprep processing rules to require use of the
UseSTD3ASCIIRules flag.
o Encouraged use of the 'from' and 'to' attributes on stream
headers.
o More fully specified stream closing handshake.
o Specified recommended stream reconnection algorithm.
o Specified return of <restricted-xml/> stream error in response to
receipt of prohibited XML features.
o Specified that SASL mechanisms must be sent both before and after
negotiation of SASL security layers.
o Specified that TLS plus SASL PLAIN is a mandatory-to-implement
technology for client-to-server connections, since implementation
of SASL EXTERNAL is uncommon in XMPP clients, in part because
underlying security features such as X.509 certificates are not
yet widely deployed.
o Added the <malformed-request/> SASL error condition to handle an
error case discussed in RFC 4422.
o More fully specified binding of multiple resources to the same
stream.
o Added the <unknown-sender/> stanza error condition to provide
appropriate handling of stanzas when multiple resources are bound
to the same stream.
o Added the <not-modified/> stanza error condition to enable
potential ETags usage.
o Removed historical documentation for the server dialback protocol
from this specification to a separate specification
In addition, numerous changes of an editorial nature were made in
order to more fully specify and clearly explain the protocols.
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Appendix G. Copying Conditions
The Contributor grants third parties the irrevocable right to copy,
use and distribute the Contribution, with or without modification, in
any medium, without royalty, provided that, unless separate
permission is granted, redistributed modified works:
1. do not contain misleading author, version, name of work, or
endorsement information, and
2. do not claim endorsement of the modified work by the Contributor,
or any organization the Contributor belongs to, the Internet
Engineering Task Force (IETF), Internet Research Task Force
(IRTF), Internet Engineering Steering Group (IESG), Internet
Architecture Board (IAB), Internet Assigned Numbers Authority
(IANA), Internet Society (ISOC), Request For Comments (RFC)
Editor, or any combination or variation of such terms (including
without limitation the IETF "4 diamonds" logo), or any terms that
are confusingly similar thereto, and
3. remove any claims of status as an Internet Standard, including
without limitation removing the RFC boilerplate.
The IETF suggests that any citation or excerpt of unmodified text
reference the RFC or other document from which the text is derived.
Index
B
Bare JID 11
C
Connected Resource 11
D
Domain Identifier 10
E
Entity 9
Error Stanza 73
Extended Content 88
F
Full JID 11
I
Initial Stream 14
IQ Stanza 72
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J
Jabber Identifier 9
M
Message Stanza 71
N
Node Identifier 11
P
Presence Stanza 71
R
Resource Identifier 11
Response Stream 14
X
XML Stanza 14
XML Stream 14
Author's Address
Peter Saint-Andre (editor)
XMPP Standards Foundation
Email: stpeter@jabber.org
URI: xmpp:stpeter@jabber.org
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Internet-Draft XMPP Core July 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
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OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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