Network Working Group P. Saint-Andre

Network Working Group P. Saint-Andre
Request for Comments: 4622 JSF
Category: Standards Track July 2006

Internationalized Resource Identifiers (IRIs)
and Uniform Resource Identifiers (URIs) for
the Extensible Messaging and Presence Protocol (XMPP)

Status of This Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2006).

Abstract

This document defines the use of Internationalized Resource
Identifiers (IRIs) and Uniform Resource Identifiers (URIs) in
identifying or interacting with entities that can communicate via the
Extensible Messaging and Presence Protocol (XMPP).

Saint-Andre Standards Track [Page 1]

RFC 4622 XMPP IRIs/URIs July 2006

Table of Contents

1. Introduction ....................................................3
1.1. Terminology ................................................3
2. Use of XMPP IRIs and URIs .......................................4
2.1. Rationale ..................................................4
2.2. Form .......................................................4
2.3. Authority Component ........................................6
2.4. Path Component .............................................7
2.5. Query Component ............................................7
2.6. Fragment Identifier Component ..............................9
2.7. Generation of XMPP IRIs/URIs ...............................9
2.7.1. Generation Method ...................................9
2.7.2. Generation Notes ...................................10
2.7.3. Generation Example .................................11
2.8. Processing of XMPP IRIs/URIs ..............................12
2.8.1. Processing Method ..................................12
2.8.2. Processing Notes ...................................13
2.8.3. Processing Example .................................14
2.9. Internationalization ......................................14
3. IANA Registration of xmpp URI Scheme ...........................15
3.1. URI Scheme Name ...........................................15
3.2. Status ....................................................15
3.3. URI Scheme Syntax .........................................15
3.4. URI Scheme Semantics ......................................16
3.5. Encoding Considerations ...................................16
3.6. Applications/protocols That Use This URI Scheme Name ......16
3.7. Interoperability Considerations ...........................16
3.8. Security Considerations ...................................16
3.9. Contact ...................................................17
3.10. Author/Change Controller .................................17
3.11. References ...............................................17
4. IANA Considerations ............................................17
5. Security Considerations ........................................17
5.1. Reliability and Consistency ...............................17
5.2. Malicious Construction ....................................18
5.3. Back-End Transcoding ......................................18
5.4. Sensitive Information .....................................18
5.5. Semantic Attacks ..........................................19
5.6. Spoofing ..................................................19
6. References .....................................................20
6.1. Normative References ......................................20
6.2. Informative References ....................................20

Saint-Andre Standards Track [Page 2]

RFC 4622 XMPP IRIs/URIs July 2006

1. Introduction

The Extensible Messaging and Presence Protocol (XMPP) is a streaming
XML technology that enables any two entities on a network to exchange
well-defined but extensible XML elements (called "XML stanzas") at a
rate close to real time.

As specified in [XMPP-CORE], entity addresses as used in
communications over an XMPP network must not be prepended with a
Uniform Resource Identifier (URI) scheme (as specified in [URI]).
However, applications external to an XMPP network may need to
identify XMPP entities either as URIs or, in a more modern fashion,
as Internationalized Resource Identifiers (IRIs; see [IRI]).
Examples of such external applications include databases that need to
store XMPP addresses and non-native user agents such as web browsers
and calendaring applications that provide interfaces to XMPP
services.

The format for an XMPP address is defined in [XMPP-CORE]. Such an
address may contain nearly any [UNICODE] character and must adhere to
various profiles of [STRINGPREP]. The result is that an XMPP address
is fully internationalizable and is very close to being an IRI
without a scheme. However, given that there is no freestanding
registry of IRI schemes, it is necessary to define XMPP identifiers
primarily as URIs rather than as IRIs, and to register an XMPP URI
scheme instead of an IRI scheme. Therefore, this document does the
following:

o Specifies how to identify XMPP entities as IRIs or URIs.

o Specifies how to interact with XMPP entities as IRIs or URIs.

o Formally defines the syntax for XMPP IRIs and URIs.

o Specifies how to transform XMPP IRIs into URIs and vice-versa.

o Registers the xmpp URI scheme.

1.1. Terminology

This document inherits terminology from [IRI], [URI], and
[XMPP-CORE].

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [TERMS].

Saint-Andre Standards Track [Page 3]

RFC 4622 XMPP IRIs/URIs July 2006

2. Use of XMPP IRIs and URIs

2.1. Rationale

As described in [XMPP-IM], instant messaging and presence
applications of XMPP must handle im: and pres: URIs (as specified by
[CPIM] and [CPP]). However, there are many other applications of
XMPP (including network management, workflow systems, generic
publish-subscribe, remote procedure calls, content syndication,
gaming, and middleware), and these applications do not implement
instant messaging and presence semantics. Neither does a generic
XMPP entity implement the semantics of any existing URI scheme, such
as the http:, ftp:, or mailto: scheme. Therefore, it is appropriate
to define a new URI scheme that makes it possible to identify or
interact with any XMPP entity (not just instant messaging and
presence entities) as an IRI or URI.

XMPP IRIs and URIs are defined for use by non-native interfaces and
applications, and primarily for the purpose of identification rather
than of interaction (on the latter distinction, see Section 1.2.2 of
[URI]). In order to ensure interoperability on XMPP networks, when
data is routed to an XMPP entity (e.g., when an XMPP address is
contained in the 'to' or 'from' attribute of an XML stanza) or an
XMPP entity is otherwise identified in standard XMPP protocol
elements, the entity MUST be addressed as <[node@]domain[/resource]>
(i.e., without a prepended scheme), where the "node identifier",
"domain identifier", and "resource identifier" portions of an XMPP
address conform to the definitions provided in Section 3 of
[XMPP-CORE].

(Note: For historical reasons, the term "resource identifier" is used
in XMPP to refer to the optional portion of an XMPP address that
follows the domain identifier and the "/" separator character (for
details, refer to Section 3.4 of [XMPP-CORE]; this use of the term
"resource identifier" is not to be confused with the meanings of
"resource" and "identifier" provided in Section 1.1 of [URI]).

2.2. Form

As described in [XMPP-CORE], an XMPP address used natively on an XMPP
network is a string of Unicode characters that (1) conforms to a
certain set of [STRINGPREP] profiles and [IDNA] restrictions, (2)
follows a certain set of syntax rules, and (3) is encoded as [UTF-8].
The form of such an address can be represented using Augmented
Backus-Naur Form ([ABNF]) as:

[ node "@" ] domain [ "/" resource ]

Saint-Andre Standards Track [Page 4]

RFC 4622 XMPP IRIs/URIs July 2006

In this context, the "node" and "resource" rules rely on distinct
profiles of [STRINGPREP], and the "domain" rule relies on the concept
of an internationalized domain name as described in [IDNA]. (Note:
There is no need to refer to punycode in the IRI syntax itself, since
any punycode representation would occur only inside an XMPP
application in order to represent internationalized domain names.
However, it is the responsibility of the processing application to
convert [IRI] syntax into [IDNA] syntax before addressing XML stanzas
to the specified entity on an XMPP network.)

Naturally, in order to be converted into an IRI or URI, an XMPP
address must be prepended with a scheme (specifically, the xmpp
scheme) and may also need to undergo transformations that adhere to
the rules defined in [IRI] and [URI]. Furthermore, in order to
enable more advanced interaction with an XMPP entity rather than
simple identification, it is desirable to take advantage of
additional aspects of URI syntax and semantics, such as authority
components, query components, and fragment identifier components.

Therefore, the ABNF syntax for an XMPP IRI is defined as shown below
using Augmented Backus-Naur Form specified by [ABNF], where the
"ifragment", "ihost", and "iunreserved" rules are defined in [IRI],
the "pct-encoded" rule is defined in [URI], and DQUOTE is defined in
[ABNF]:

xmppiri = "xmpp" ":" ihierxmpp
[ "?" iquerycomp ]
[ "#" ifragment ]
ihierxmpp = iauthpath / ipathxmpp
iauthpath = "//" iauthxmpp [ "/" ipathxmpp ]
iauthxmpp = inodeid "@" ihost
ipathxmpp = [ inodeid "@" ] ihost [ "/" iresid ]
inodeid = *( iunreserved / pct-encoded / nodeallow )
nodeallow = "!" / "$" / "(" / ")" / "*" / "+" / "," / ";" /
"=" / "[" / "\" / "]" / "^" / "`" / "{" / "|" /
"}"
iresid = *( iunreserved / pct-encoded / resallow )
resallow = "!" / DQUOTE / "$" / "&" / "'" / "(" / ")" /
"*" / "+" / "," / ":" / ";" / "<" / "=" / ">" /
"[" / "\" / "]" / "^" / "`" / "{" / "|" / "}"
iquerycomp = iquerytype [ *ipair ]
iquerytype = *iunreserved
ipair = ";" ikey "=" ivalue
ikey = *iunreserved
ivalue = *( iunreserved / pct-encoded )

Saint-Andre Standards Track [Page 5]

RFC 4622 XMPP IRIs/URIs July 2006

However, the foregoing syntax is not appropriate for inclusion in the
registration of the xmpp URI scheme, since the IANA recognizes only
URI schemes and not IRI schemes. Therefore, the ABNF syntax for an
XMPP URI rather than for IRI is defined as shown in Section 3.3 of
this document (see below under "IANA Registration"). If it is
necessary to convert the IRI syntax into URI syntax, an application
MUST adhere to the mapping procedure specified in Section 3.1 of
[IRI].

The following is an example of a basic XMPP IRI/URI used for purposes
of identifying a node associated with an XMPP server:

xmpp:[email protected]

Descriptions of the various components of an XMPP IRI/URI are
provided in the following sections.

2.3. Authority Component

As explained in Section 2.8 of this document, in the absence of an
authority component, the processing application would authenticate as
a configured user at a configured XMPP server. That is, the
authority component section is unnecessary and should be ignored if
the processing application has been configured with a set of default
credentials.

In accordance with Section 3.2 of RFC 3986, the authority component
is preceded by a double slash ("//") and is terminated by the next
slash ("/"), question mark ("?"), or number sign ("#") character, or
by the end of the IRI/URI. As explained more fully in Section 2.8.1
of this document, the presence of an authority component signals the
processing application to authenticate as the node@domain specified
in the authority component rather than as a configured node@domain
(see the Security Considerations section of this document regarding
authentication). (While it is unlikely that the authority component
will be included in most XMPP IRIs or URIs, the scheme allows for its
inclusion, if appropriate.) Thus, the following XMPP IRI/URI
indicates to authenticate as "[email protected]":

xmpp://[email protected]

Note well that this is quite different from the following XMPP
IRI/URI, which identifies a node "[email protected]" but does not
signal the processing application to authenticate as that node:

xmpp:[email protected]

Saint-Andre Standards Track [Page 6]

RFC 4622 XMPP IRIs/URIs July 2006

Similarly, using a possible query component of "?message" to trigger
an interface for sending a message, the following XMPP IRI/URI
signals the processing application to authenticate as
"[email protected]" and to send a message to "[email protected]":

xmpp://[email protected]/[email protected]?message

By contrast, the following XMPP IRI/URI signals the processing
application to authenticate as its configured default account and to
send a message to "[email protected]":

xmpp:[email protected]?message

2.4. Path Component

The path component of an XMPP IRI/URI identifies an XMPP address or
specifies the XMPP address to which an XML stanza shall be directed
at the end of IRI/URI processing.

For example, the following XMPP IRI/URI identifies a node associated
with an XMPP server:

xmpp:[email protected]

The following XMPP IRI/URI identifies a node associated with an XMPP
server along with a particular XMPP resource identifier associated
with that node:

xmpp:[email protected]/some-resource

Inclusion of a node is optional in XMPP addresses, so the following
XMPP IRI/URI simply identifies an XMPP server:

xmpp:example.com

2.5. Query Component

There are many potential use cases for encapsulating information in
the query component of an XMPP IRI/URI; examples include but are not
limited to:

o sending an XMPP message stanza (see [XMPP-IM]),

o adding a roster item (see [XMPP-IM]),

o sending a presence subscription (see [XMPP-IM]),

o probing for current presence information (see [XMPP-IM]),

Saint-Andre Standards Track [Page 7]

RFC 4622 XMPP IRIs/URIs July 2006

o triggering a remote procedure call (see [JEP-0009]),

o discovering the identity or capabilities of another entity (see
[JEP-0030]),

o joining an XMPP-based text chat room (see [JEP-0045]),

o interacting with publish-subscribe channels (see [JEP-0060]),

o providing a SOAP interface (see [JEP-0072]), and

o registering with another entity (see [JEP-0077]).

Many of these potential use cases are application specific, and the
full range of such applications cannot be foreseen in advance given
the continued expansion in XMPP development; however, there is
agreement within the Jabber/XMPP developer community that all the
uses envisioned to date can be encapsulated via a "query type",
optionally supplemented by one or more "key-value" pairs (this is
similar to the "application/x-www-form-urlencoded" MIME type
described in [HTML]).

As an example, an XMPP IRI/URI intended to launch an interface for
sending a message to the XMPP entity "[email protected]" might
be represented as follows:

xmpp:[email protected]?message

Similarly, an XMPP IRI/URI intended to launch an interface for
sending a message to the XMPP entity "[email protected]" with
a particular subject might be represented as follows:

xmpp:[email protected]?message;subject=Hello%20World

If the processing application does not understand query components or
the specified query type, it MUST ignore the query component and
treat the IRI/URI as consisting of, for example,
<xmpp:[email protected]> rather than
<xmpp:[email protected]?query>. If the processing application
does not understand a particular key within the query component, it
MUST ignore that key and its associated value.

As noted, there exist many kinds of XMPP applications (both actual
and potential), and such applications may define query types and keys
for use in the query component portion of XMPP URIs. The Jabber
Registrar function (see [JEP-0053]) of the Jabber Software Foundation
maintains a registry of such query types and keys at
<http://www.jabber.org/registrar/querytypes.html>. To help ensure

Saint-Andre Standards Track [Page 8]

RFC 4622 XMPP IRIs/URIs July 2006

interoperability, any application using the formats defined in this
document SHOULD submit any associated query types and keys to that
registry in accordance with the procedures specified in [JEP-0147].

2.6. Fragment Identifier Component

As stated in Section 3.5 of [URI], "The fragment identifier component
of a URI allows indirect identification of a secondary resource by
reference to a primary resource and additional identifying
information." Because the resource identified by an XMPP IRI/URI
does not make available any media type (see [MIME]) and therefore (in
the terminology of [URI]) no representation exists at an XMPP
resource, the semantics of the fragment identifier component in XMPP
IRIs/URIs are to be "considered unknown and, effectively,
unconstrained" (ibid.). Particular XMPP applications MAY make use of
the fragment identifier component for their own purposes. However,
if a processing application does not understand fragment identifier
components or the syntax of a particular fragment identifier
component included in an XMPP IRI/URI, it MUST ignore the fragment
identifier component.

2.7. Generation of XMPP IRIs/URIs

2.7.1. Generation Method

In order to form an XMPP IRI from an XMPP node identifier, domain
identifier, and resource identifier, the generating application MUST
first ensure that the XMPP address conforms to the rules specified in
[XMPP-CORE], including application of the relevant [STRINGPREP]; it
MUST then concatenate the following:

1. The "xmpp" scheme and the ":" character

2. Optionally (if an authority component is to be included before
the node identifier), the characters "//", an authority component
of the form node@domain, and the character "/".

3. Optionally (if the XMPP address contained an XMPP "node
identifier"), a string of Unicode characters that conforms to the
"inodeid" rule, followed by the "@" character.

4. A string of Unicode characters that conforms to the "ihost" rule.

5. Optionally (if the XMPP address contained an XMPP "resource
identifier"), the character "/" and a string of Unicode
characters that conforms to the "iresid" rule.

Saint-Andre Standards Track [Page 9]

RFC 4622 XMPP IRIs/URIs July 2006

6. Optionally (if a query component is to be included), the "?"
character and query component.

7. Optionally (if a fragment identifier component is to be
included), the "#" character and fragment identifier component.

In order to form an XMPP URI from the resulting IRI, an application
MUST adhere to the mapping procedure specified in Section 3.1 of
[IRI].

2.7.2. Generation Notes

Certain characters are allowed in the node identifier, domain
identifier, and resource identifier portions of a native XMPP address
but prohibited by the "inodeid", "ihost", and "iresid" rules of an
XMPP IRI. Specifically, the "#" and "?" characters are allowed in
node identifiers, and the "/", "?", "#", and "@" characters are
allowed in resource identifiers, but these characters are used as
delimiters in XMPP IRIs. In addition, the " " ([US-ASCII] space)
character is allowed in resource identifiers but prohibited in IRIs.
Therefore, all the foregoing characters MUST be percent-encoded when
transforming an XMPP address into an XMPP IRI.

Consider the following nasty node in an XMPP address:

nasty!#$%()*+,-.;=?[\]^_`{|}[email protected]

That address would be transformed into the following XMPP IRI:

xmpp:nasty!%23$%25()*+,-.;=%3F[\]^_`{|}[email protected]

Consider the following repulsive resource in an XMPP address (split
into two lines for layout purposes):

[email protected]
/repulsive !#"$%&'()*+,-./:;<=>?@[\]^_`{|}~resource

That address would be transformed into the following XMPP IRI (split
into two lines for layout purposes):

xmpp:[email protected]
/repulsive%20!%23"$%25&'()*+,-.%2F:;<=>%3F%40[\]^_`{|}~resource

Furthermore, virtually any character outside the [US-ASCII] range is
allowed in an XMPP address and therefore also in an XMPP IRI, but URI
syntax forbids such characters directly and specifies that such
characters MUST be percent-encoded. In order to determine the URI
associated

Saint-Andre Standards Track [Page 10]

RFC 4622 XMPP IRIs/URIs July 2006

with an XMPP IRI, an application MUST adhere to the mapping procedure
specified in Section 3.1 of [IRI].

2.7.3. Generation Example

Consider the following XMPP address:

<jiři@čechy.example/v Praze>

Note: The string "ř" stands for the Unicode character LATIN
SMALL LETTER R WITH CARON, and the string "č" stands for the
Unicode character LATIN SMALL LETTER C WITH CARON, following the "XML
Notation" used in [IRI] to represent characters that cannot be
rendered in ASCII-only documents (note also that these characters are
represented in their stringprep canonical form). The '<' and '>'
characters are not part of the address itself but are provided to set
off the address for legibility. For those who do not read Czech,
this example could be Anglicized as "[email protected]/In
Prague".

In accordance with the process specified above, the generating
application would do the following to generate a valid XMPP IRI from
this address:

1. Ensure that the XMPP address conforms to the rules specified in
[XMPP-CORE], including application of the relevant [STRINGPREP]
profiles and encoding as a [UTF-8] string.

2. Concatenate the following:

1. The "xmpp" scheme and the ":" character.

2. An "authority component" if included (not shown in this
example).

3. A string of Unicode characters that represents the XMPP
address, transformed in accordance with the "inodeid",
"ihost", and "iresid" rules.

4. The "?" character followed by a "query component", if
appropriate to the application (not shown in this example).

5. The "#" character followed by a "fragment identifier
component", if appropriate to the application (not shown in
this example).

Saint-Andre Standards Track [Page 11]

RFC 4622 XMPP IRIs/URIs July 2006

The result is this XMPP IRI:

<xmpp:jiři@čechy.example/v%20Praze>

In order to generate a valid XMPP URI from the foregoing IRI, the
application MUST adhere to the procedure specified in Section 3.1 of
[IRI], resulting in the following URI:

<xmpp:ji%C5%99i@%C4%8Dechy.example/v%20Praze>

2.8. Processing of XMPP IRIs/URIs

2.8.1. Processing Method

If a processing application is presented with an XMPP URI and not
with an XMPP IRI, it MUST first convert the URI into an IRI by
following the procedure specified in Section 3.2 of [IRI].

In order to decompose an XMPP IRI for interaction with the entity it
identifies, a processing application MUST separate:

1. The "xmpp" scheme and the ":" character.

2. The authority component, if included (the string of Unicode
characters between the "//" characters and the next "/"
character, the "?" character, the "#" character, or the end of
the IRI).

3. A string of Unicode characters that represents an XMPP address as
transformed in accordance with the "inodeid", "ihost", and
"iresid" rules.

4. Optionally the query component, if included, using the "?"
character as a separator.

5. Optionally the fragment identifier component, if included, using
the "#" character as a separator.

At this point, the processing application MUST ensure that the
resulting XMPP address conforms to the rules specified in
[XMPP-CORE], including application of the relevant [STRINGPREP]. The
processing application then would either (1) complete further XMPP
handling itself or (2) invoke a helper application to complete XMPP
handling; such XMPP handling would most likely consist of the
following steps:

Saint-Andre Standards Track [Page 12]

RFC 4622 XMPP IRIs/URIs July 2006

1. If not already connected to an XMPP server, connect either as the
user specified in the authority component or as the configured
user at the configured XMPP server, normally by adhering to the
XMPP connection procedures defined in [XMPP-CORE]. (Note: The
processing application SHOULD ignore the authority component if
it has been configured with a set of default credentials.)

2. Optionally, determine the nature of the intended recipient (e.g.,
via [JEP-0030]).

3. Optionally, present an appropriate interface to a user based on
the nature of the intended recipient and/or the contents of the
query component.

4. Generate an XMPP stanza that translates any user or application
inputs into their corresponding XMPP equivalents.

5. Send the XMPP stanza via the authenticated server connection for
delivery to the intended recipient.

2.8.2. Processing Notes

It may help implementors to note that the first two steps of "further
XMPP handling", as described at the end of Section 2.8.1, are similar
to HTTP authentication ([HTTP-AUTH]), while the next three steps are
similar to the handling of mailto: URIs ([MAILTO]).

As noted in Section 2.7.2 of this document, certain characters are
allowed in the node identifier, domain identifier, and resource
identifier portions of a native XMPP address but prohibited by the
"inodeid", "ihost", and "iresid" rules of an XMPP IRI. The
percent-encoded octets corresponding to these characters in XMPP IRIs
MUST be transformed into the characters allowed in XMPP addresses
when processing an XMPP IRI for interaction with the represented XMPP
entity.

Consider the following nasty node in an XMPP IRI:

xmpp:nasty!%23$%()*+,-.;=%3F[\]^_`{|}[email protected]

That IRI would be transformed into the following XMPP address:

nasty!#$%()*+,-.;=?[\]^_`{|}[email protected]

Saint-Andre Standards Track [Page 13]

RFC 4622 XMPP IRIs/URIs July 2006

Consider the following repulsive resource in an XMPP IRI (split into
two lines for layout purposes):

xmpp:[email protected]
/repulsive%20!%23"$%25&'()*+,-.%2F:;<=>%3F%40[\]^_`{|}~resource

That IRI would be transformed into the following XMPP address (split
into two lines for layout purposes):

[email protected]
/repulsive !#"$%&'()*+,-./:;<=>?@[\]^_`{|}~resource

2.8.3. Processing Example

Consider the XMPP URI that resulted from the previous example:

<xmpp:ji%C5%99i@%C4%8Dechy.example/v%20Praze>

In order to generate a valid XMPP IRI from that URI, the application
MUST adhere to the procedure specified in Section 3.2 of [IRI],
resulting in the following IRI:

<xmpp:jiři@čechy.example/v%20Praze>

In accordance with the process specified above, the processing
application would remove the "xmpp" scheme and ":" character to
extract the XMPP address from this XMPP IRI, converting any
percent-encoded octets from the "inodeid", "ihost", and "iresid"
rules into their character equivalents (e.g., "%20" into the space
character).

The result is this XMPP address:

<jiři@čechy.example/v Praze>

2.9. Internationalization

Because XMPP addresses are [UTF-8] strings and because octets outside
the [US-ASCII] range within XMPP addresses can be easily converted to
percent-encoded octets, XMPP addresses are designed to work well with
Internationalized Resource Identifiers ([IRI]). In particular, with
the exceptions of stringprep verification, the conversion of
syntax-relevant [US-ASCII] characters (e.g., "?"), and the conversion
of percent-encoded octets from the "inodeid", "ihost", and "iresid"
rules into their character equivalents (e.g., "%20" into the
[US-ASCII] space character), an XMPP IRI can be constructed directly
by prepending the "xmpp" scheme and ":" character to an XMPP address.
Furthermore, an XMPP IRI can be converted into URI syntax by adhering

Saint-Andre Standards Track [Page 14]

RFC 4622 XMPP IRIs/URIs July 2006

to the procedure specified in Section 3.1 of [IRI], and an XMPP URI
can be converted into IRI syntax by adhering to the procedure
specified in Section 3.2 of [IRI], thus ensuring interoperability
with applications that are able to process URIs but unable to process
IRIs.

3. IANA Registration of xmpp URI Scheme

In accordance with [URI-SCHEMES], this section provides the
information required to register the xmpp URI scheme.

3.1. URI Scheme Name

xmpp

3.2. Status

permanent

3.3. URI Scheme Syntax

The syntax for an xmpp URI is defined below using Augmented
Backus-Naur Form as specified by [ABNF], where the "fragment",
"host", "pct-encoded", and "unreserved" rules are defined in [URI]
and DQUOTE is defined in [ABNF]:

xmppuri = "xmpp" ":" hierxmpp [ "?" querycomp ] [ "#" fragment ]
hierxmpp = authpath / pathxmpp
authpath = "//" authxmpp [ "/" pathxmpp ]
authxmpp = nodeid "@" host
pathxmpp = [ nodeid "@" ] host [ "/" resid ]
nodeid = *( unreserved / pct-encoded / nodeallow )
nodeallow = "!" / "$" / "(" / ")" / "*" / "+" / "," / ";" /
"=" / "[" / "\" / "]" / "^" / "`" / "{" / "|" /
"}"
resid = *( unreserved / pct-encoded / resallow )
resallow = "!" / DQUOTE / "$" / "&" / "'" / "(" / ")" /
"*" / "+" / "," / ":" / ";" / "<" / "=" / ">" /
"[" / "\" / "]" / "^" / "`" / "{" / "|" / "}"
querycomp = querytype [ *pair ]
querytype = *( unreserved / pct-encoded )
pair = ";" key "=" value
key = *( unreserved / pct-encoded )
value = *( unreserved / pct-encoded )

Saint-Andre Standards Track [Page 15]

RFC 4622 XMPP IRIs/URIs July 2006

3.4. URI Scheme Semantics

The xmpp URI scheme identifies entities that natively communicate
using the Extensible Messaging and Presence Protocol (XMPP), and is
mainly used for identification rather than for resource location.
However, if an application that processes an xmpp URI enables
interaction with the XMPP address identified by the URI, it MUST
follow the methodology defined in Section 2 of RFC 4622, Use of XMPP
IRIs and URIs, to reconstruct the encapsulated XMPP address, connect
to an appropriate XMPP server, and send an appropriate XMPP "stanza"
(XML fragment) to the XMPP address. (Note: There is no MIME type
associated with the xmpp URI scheme.)

3.5. Encoding Considerations

In addition to XMPP URIs, there will also be XMPP Internationalized
Resource Identifiers (IRIs). Prior to converting an Extensible
Messaging and Presence Protocol (XMPP) address into an IRI (and in
accordance with [XMPP-CORE]), the XMPP address must be represented as
[UTF-8] by the generating application (e.g., by transforming an
application's internal representation of the address as a UTF-16
string into a UTF-8 string), and the UTF-8 string must then be
prepended with the "xmpp" scheme and ":" character. However, because
an XMPP URI must contain only [US-ASCII] characters, the UTF-8 string
of an XMPP IRI must be transformed into URI syntax by adhering to the
procedure specified in RFC 3987.

3.6. Applications/protocols That Use This URI Scheme Name

The xmpp URI scheme is intended to be used by interfaces to an XMPP
network from non-native user agents, such as web browsers, as well as
by non-native applications that need to identify XMPP entities as
full URIs or IRIs.

3.7. Interoperability Considerations

There are no known interoperability concerns related to use of the
xmpp URI scheme. In order to help ensure interoperability, the
Jabber Registrar function of the Jabber Software Foundation maintains
a registry of query types and keys that can be used in the query
components of XMPP URIs and IRIs, located at
<http://www.jabber.org/registrar/querytypes.html>.

3.8. Security Considerations

See Section 5 of RFC 4622, Security Considerations.

Saint-Andre Standards Track [Page 16]

RFC 4622 XMPP IRIs/URIs July 2006

3.9. Contact

Peter Saint-Andre [mailto:[email protected],
xmpp:[email protected]]

3.10. Author/Change Controller

This scheme is registered under the IETF tree. As such, the IETF
maintains change control.

3.11. References

[XMPP-CORE]

4. IANA Considerations

This document registers a URI scheme. The registration template can
be found in Section 3 of this document. In order to help ensure
interoperability, the Jabber Registrar function of the Jabber
Software Foundation maintains a registry of query types and keys that
can be used in the query components of XMPP URIs and IRIs, located at
<http://www.jabber.org/registrar/querytypes.html>.

5. Security Considerations

Providing an interface to XMPP services from non-native applications
introduces new security concerns. The security considerations
discussed in [IRI], [URI], and [XMPP-CORE] apply to XMPP IRIs, and
the security considerations discussed in [URI] and [XMPP-CORE] apply
to XMPP URIs. In accordance with Section 2.7 of [URI-SCHEMES] and
Section 7 of [URI], particular security considerations are specified
in the following sections.

5.1. Reliability and Consistency

Given that XMPP addresses of the form [email protected] are typically
created via registration at an XMPP server or provisioned by an
administrator of such a server, it is possible that such addresses
may also be unregistered or deprovisioned. Therefore, the XMPP
IRI/URI that identifies such an XMPP address may not be reliably and
consistently associated with the same principal, account owner,
application, or device.

XMPP addresses of the form [email protected]/resource are typically
even more ephemeral (since a given XMPP resource identifier is
typically associated with a particular, temporary session of an XMPP
client at an XMPP server); therefore the XMPP IRI/URI that identifies
such an XMPP address probably will not reliably and consistently be

Saint-Andre Standards Track [Page 17]

RFC 4622 XMPP IRIs/URIs July 2006

associated with the same session. However, the procedures specified
in Section 10 of [XMPP-CORE] effectively eliminate any potential
confusion that might be introduced by the lack of reliability and
consistency for the XMPP IRI/URI that identifies such an XMPP
address.

XMPP addresses of the form domain.tld are typically long-lived XMPP
servers or associated services; although naturally it is possible for
server or service administrators to de-commission the server or
service at any time, typically the IRIs/URIs that identify such
servers or services are the most reliable and consistent of XMPP
IRIs/URIs.

XMPP addresses of the form domain.tld/resource are not yet common on
XMPP networks; however, the reliability and consistency of XMPP
IRIs/URIs that identify such XMPP addresses would likely fall
somewhere between those that identify XMPP addresses of the form
domain.tld and those that identify XMPP addresses of the form
[email protected].

5.2. Malicious Construction

Malicious construction of XMPP IRIs/URIs is made less likely by the
prohibition on port numbers in XMPP IRIs/URIs (since port numbers are
to be discovered using [DNS-SRV] records, as specified in
[XMPP-CORE]).

5.3. Back-End Transcoding

Because the base XMPP protocol is designed to implement the exchange
of messages and presence information and not the retrieval of files
or invocation of similar system functions, it is deemed unlikely that
the use of XMPP IRIs/URIs would result in harmful dereferencing.
However, if an XMPP protocol extension defines methods for
information retrieval, it MUST define appropriate controls over
access to that information. In addition, XMPP servers SHOULD NOT
natively parse XMPP IRIs/URIs but instead SHOULD accept only the XML
wire protocol specified in [XMPP-CORE] and any desired extensions
thereto.

5.4. Sensitive Information

The ability to interact with XMPP entities via a web browser or other
non-native application may expose sensitive information (such as
support for particular XMPP application protocol extensions) and
thereby make it possible to launch attacks that are not possible or
that are unlikely on a native XMPP network. Due care must be taken

Saint-Andre Standards Track [Page 18]

RFC 4622 XMPP IRIs/URIs July 2006

in deciding what information is appropriate for representation in
XMPP IRIs or URIs.

In particular, advertising XMPP IRIs/URIs in publicly accessible
locations (e.g., on websites) may make it easier for malicious users
to harvest XMPP addresses from the authority and path components of
XMPP IRIs/URIs and therefore to send unsolicited bulk communications
to the users or applications represented by those addresses. Due
care should be taken in balancing the benefits of open information
exchange against the potential costs of unwanted communications.

To help prevent leaking of sensitive information, passwords and other
user credentials are forbidden in the authority component of XMPP
IRIs/URIs; in fact they are not needed, since the fact that
authentication in XMPP occurs via [SASL] makes it possible to use the
SASL ANONYMOUS mechanism, if desired.

5.5. Semantic Attacks

Despite the existence of non-hierarchical URI schemes such as
[MAILTO], by association human users may expect all URIs to include
the "//" characters after the scheme name and ":" character.
However, in XMPP IRIs/URIs, the "//" characters precede the authority
component rather than the path component. Thus,
xmpp://[email protected] indicates to authenticate as
"[email protected]", whereas xmpp:[email protected] identifies the
node "[email protected]". Processing applications MUST clearly
differentiate between these forms, and user agents SHOULD discourage
human users from including the "//" characters in XMPP IRIs/URIs
since use of the authority component is envisioned to be helpful only
in specialized scenarios, not more generally.

5.6. Spoofing

The ability to include effectively the full range of Unicode
characters in an XMPP IRI may make it easier to execute certain forms
of address mimicking (also called "spoofing"). However, XMPP IRIs
are no different from other IRIs in this regard, and applications
that will present XMPP IRIs to human users must adhere to best
practices regarding address mimicking in order to help prevent
attacks that result from spoofed addresses (e.g., the phenomenon
known as "phishing"). For details, refer to the Security
Considerations of [IRI].

Saint-Andre Standards Track [Page 19]

RFC 4622 XMPP IRIs/URIs July 2006

6. References

6.1. Normative References

[ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.

[IRI] Duerst, M. and M. Suignard, "Internationalized
Resource Identifiers (IRIs)", RFC 3987, January 2005.

[TERMS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[URI] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic Syntax",
STD 66, RFC 3986, January 2005.

[XMPP-CORE] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004.

6.2. Informative References

[CPIM] Peterson, J., "Common Profile for Instant Messaging
(CPIM)", RFC 3860, August 2004.

[CPP] Peterson, J., "Common Profile for Presence (CPP)",
RFC 3859, August 2004.

[DNS-SRV] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR
for specifying the location of services (DNS SRV)",
RFC 2782, February 2000.

[HTML] Raggett, D., "HTML 4.0 Specification", W3C
REC REC-html40-19980424, April 1998.

[HTTP-AUTH] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence,
S., Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access
Authentication", RFC 2617, June 1999.

[IDNA] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications
(IDNA)", RFC 3490, March 2003.

[JEP-0009] Adams, D., "Jabber-RPC", JSF JEP 0009, February 2006.

Saint-Andre Standards Track [Page 20]

RFC 4622 XMPP IRIs/URIs July 2006

[JEP-0030] Hildebrand, J., Millard, P., Eatmon, R., and P.
Saint-Andre, "Service Discovery", JSF JEP 0030,
January 2006.

[JEP-0045] Saint-Andre, P., "Multi-User Chat", JSF JEP 0045,
September 2005.

[JEP-0053] Saint-Andre, P., "Jabber Registrar", JSF JEP 0053,
May 2004.

[JEP-0060] Millard, P., Saint-Andre, P., and R. Meijer,
"Publish-Subscribe", JSF JEP 0060, June 2005.

[JEP-0072] Forno, F. and P. Saint-Andre, "SOAP Over XMPP", JSF
JEP 0072, December 2005.

[JEP-0077] Saint-Andre, P., "In-Band Registration", JSF JEP 0077,
January 2006.

[JEP-0147] Saint-Andre, P., "XMPP IRI/URI Query Components", JSF
JEP 0147, March 2006.

[MAILTO] Hoffman, P., Masinter, L., and J. Zawinski, "The
mailto URL scheme", RFC 2368, July 1998.

[MIME] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part Two: Media Types",
RFC 2046, November 1996.

[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.

[UNICODE] The Unicode Consortium, "The Unicode Standard, Version
3.2.0", 2000.

The Unicode Standard, Version 3.2.0 is defined by The
Unicode Standard, Version 3.0 (Reading, MA, Addison-
Wesley, 2000. ISBN 0-201-61633-5), as amended by the
Unicode Standard Annex #27: Unicode 3.1
(http://www.unicode.org/reports/tr27/) and by the
Unicode Standard Annex #28: Unicode 3.2
(http://www.unicode.org/reports/tr28/).

Saint-Andre Standards Track [Page 21]

RFC 4622 XMPP IRIs/URIs July 2006

[URI-SCHEMES] Hansen, T., Hardie, T., and L. Masinter, "Guidelines
and Registration Procedures for New URI Schemes",
RFC 4395, February 2006.

[US-ASCII] American National Standards Institute, "Coded
Character Set - 7-bit American Standard Code for
Information Interchange", ANSI X3.4, 1986.

[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.

[XMPP-IM] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
RFC 3921, October 2004.

Author's Address

Peter Saint-Andre
Jabber Software Foundation

EMail: [email protected]
URI: xmpp:[email protected]

Saint-Andre Standards Track [Page 22]

RFC 4622 XMPP IRIs/URIs July 2006

Full Copyright Statement

Copyright (C) The Internet Society (2006).

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 AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.

Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
[email protected].

Acknowledgement

Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).

Saint-Andre Standards Track [Page 23]