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Versions: 00 01 02 03 04 RFC 4622

Network Working Group                                     P. Saint-Andre
Internet-Draft                                                       JSF
Expires: April 2, 2006                                September 29, 2005


   Internationalized Resource Identifiers (IRIs) and Uniform Resource
 Identifiers (URIs) for the Extensible Messaging and Presence Protocol
                                 (XMPP)
                      draft-saintandre-xmpp-iri-02

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Copyright Notice

   Copyright (C) The Internet Society (2005).

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).






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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1   Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Use of XMPP IRIs and URIs  . . . . . . . . . . . . . . . . . .  3
     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  . . . . . . . . . . . . . .  8
     2.7   Generation of XMPP IRIs/URIs . . . . . . . . . . . . . . .  9
     2.8   Processing of XMPP IRIs/URIs . . . . . . . . . . . . . . . 11
     2.9   Internationalization . . . . . . . . . . . . . . . . . . . 13
   3.  IANA Registration of xmpp: URI Scheme  . . . . . . . . . . . . 14
     3.1   URI scheme name  . . . . . . . . . . . . . . . . . . . . . 14
     3.2   URI scheme syntax  . . . . . . . . . . . . . . . . . . . . 14
     3.3   Character encoding considerations  . . . . . . . . . . . . 15
     3.4   Intended usage . . . . . . . . . . . . . . . . . . . . . . 15
     3.5   Applications and/or protocols which use this scheme
           name . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     3.6   Security considerations  . . . . . . . . . . . . . . . . . 15
     3.7   Relevant publications  . . . . . . . . . . . . . . . . . . 15
     3.8   Person and email address to contact for further
           information  . . . . . . . . . . . . . . . . . . . . . . . 15
     3.9   Author/change controller . . . . . . . . . . . . . . . . . 15
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     6.1   Normative References . . . . . . . . . . . . . . . . . . . 16
     6.2   Informative References . . . . . . . . . . . . . . . . . . 17
       Author's Address . . . . . . . . . . . . . . . . . . . . . . . 19
       Intellectual Property and Copyright Statements . . . . . . . . 20


















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

2.  Use of XMPP IRIs and URIs






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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 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 ]

   In this context, the "node" and "resource" rules rely on distinct
   profiles of [STRINGPREP] and the "domain" rule relies on the concept



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   of an internationalized domain name as described in [IDNA] (however,
   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).

   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 as specified by [ABNF], where the
   "ifragment", "ihost", and "iunreserved" rules are defined in [IRI]
   and the "pct-encoded" rule is defined in [URI]:

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

   However, the foregoing syntax is not appropriate for inclusion in the
   registration of the xmpp: URI scheme, since the IANA recognizes only
   URI schemes rather than IRI schemes.  Therefore, the ABNF syntax for
   an XMPP URI rather than IRI is defined as shown in Section 3.2
   section 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



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   of identifying a node associated with an XMPP server:

      xmpp:node@example.com

   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.
   (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 "guest@example.com":

      xmpp://guest@example.com

   Note well that this is quite different from the following XMPP IRI/
   URI, which identifies a node "guest@example.com" but does not signal
   the processing application to authenticate as that node:

      xmpp:guest@example.com

   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
   "guest@example.com" and send a message to "support@example.com":

      xmpp://guest@example.com/support@example.com?message

   By contrast, the following XMPP IRI/URI signals the processing
   application to authenticate as its configured default account and
   send a message to "support@example.com":

      xmpp:support@example.com?message



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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:example-node@example.com

   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:example-node@example.com/some-resource

   Inclusion of a node is optional in XMPP addresses, so that 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]).
   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]).
   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 of 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



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   described in [HTML]).

   As an example, an XMPP IRI/URI intended to launch an interface for
   sending a message to the XMPP entity "example-node@example.com" might
   be represented as follows:

      xmpp:example-node@example.com?message

   Similarly, an XMPP IRI/URI intended to launch an interface for
   sending a message to the XMPP entity "example-node@example.com" with
   a particular subject might be represented as follows:

      xmpp:example-node@example.com?message;subject=Hello%20World

   If included in an XMPP IRI, the query component MUST first be encoded
   as a [UTF-8] string and then (if necessary) transformed to conform to
   the "iquerycomp" rule specified above; if included in an XMPP URI,
   the query component MUST be transformed to conform to the "querycomp"
   rule specified in Section 3.2 of this document.

   If the processing application does not understand query components,
   it MUST ignore the query component and treat the IRI/URI as
   consisting of, for example, <xmpp:example-node@example.com> rather
   than <xmpp:example-node@example.com?query>.  If the processing
   application does not understand a particular key within the query
   component, it MUST ignore that key and its associated value.

   (Note: In pursuit of interoperability, it may be helpful to maintain
   a registry of query types and perhaps even of keys for use in XMPP
   query components.  Given that such values will most likely be
   specific to particular applications of XMPP rather than core to XMPP
   itself, it seems reasonable that such a registry, if created, would
   be maintained by the Jabber Registrar function of the Jabber Software
   Foundation as described in [JEP-0053], rather than by the IANA.  A
   proposal for creating such a registry can be found 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,



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   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.

   If included in an XMPP IRI, the fragment identifier component MUST
   first be encoded as a [UTF-8] string and then (if necessary)
   transformed to conform to the "ifragment" rule defined in [IRI]; if
   included in an XMPP URI, the fragment identifier component MUST be
   transformed to conform to the "fragment" rule defined in [URI].

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
   concatenate:

   1.  the "xmpp:" scheme
   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
   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)



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   character is allowed in resource identifiers but prohibited in IRIs.
   Therefore, all of 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!#$%()*+,-.;=?[\]^_`{|}~node@example.com

   That address would be transformed into the following XMPP IRI:

      xmpp:nasty!%23$%()*+,-.;=%3F[\]^_`{|}~node@example.com

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

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

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

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

   Furthermore, virtually any non-US-ASCII character 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
   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:

         <ji&#x159;i@&#x10D;echy.example/v Praze>

   (Note: The string "&#x159;" stands for the Unicode character LATIN
   SMALL LETTER R WITH CARON and the string "&#x10D;" 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 "george@czech-lands.example/In
   Prague".)




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   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
       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)

   The result is this XMPP IRI:

       <xmpp:ji&#x159;i@&#x10D;echy.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 rather than
   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
   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)




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   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 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:

   1.  If not already connected to an XMPP server, connecting 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 determining the nature of the intended recipient
       (e.g., via [JEP-0030]).
   3.  Optionally presenting an appropriate interface to a user based on
       the nature of the intended recipient and/or the contents of the
       query component.
   4.  Generating an XMPP stanza that translates any user or application
       inputs into their corresponding XMPP equivalents.
   5.  Sending 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:




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      xmpp:nasty!%23$%()*+,-.;=%3F[\]^_`{|}~node@example.com

   That IRI would be transformed into the following XMPP address:

      nasty!#$%()*+,-.;=?[\]^_`{|}~node@example.com

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

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

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

      node@example.com
      /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:ji&#x159;i@&#x10D;echy.example/v%20Praze>

   In accordance with the process specified above, the processing
   application would remove the "xmpp:" scheme 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:

       <ji&#x159;i@&#x10D;echy.example/v Praze>


2.9  Internationalization

   Because XMPP addresses are [UTF-8] strings and because the non-US-
   ASCII octets in 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



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   the exception 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 "xmpp:" to an XMPP address.  Furthermore, an XMPP IRI can
   be converted into URI syntax by adhering 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

   This section provides the information required to register the xmpp:
   URI scheme.

3.1  URI scheme name

   xmpp

3.2  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]:

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






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3.3  Character 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 an xmpp: scheme.  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.

3.4  Intended usage

   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 processing.  However, an
   application that processes an xmpp: URI SHOULD reconstruct the
   encapsulated XMPP address, connect to the appropriate XMPP server,
   and send an appropriate XMPP "stanza" (XML fragment) to the XMPP
   address.  There is no MIME type associated with the xmpp: URI scheme.

3.5  Applications and/or protocols which use this 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.

3.6  Security considerations

   See Security Considerations (Section 5) of XXXX.

3.7  Relevant publications

   [XMPP-CORE]

3.8  Person and email address to contact for further information

   Peter Saint-Andre [mailto:stpeter@jabber.org]

3.9  Author/change controller

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




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4.  IANA Considerations

   This document registers a URI scheme.  The registration template can
   be found in Section 3 of this document.

5.  Security Considerations

   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.

   Providing an interface to XMPP services from non-native applications
   introduces new security concerns.  For example, the ability to
   interact with XMPP entities via a web browser may expose sensitive
   information to attacks that are not possible or that are unlikely on
   a native XMPP network.  Due care must be taken in deciding what
   information is appropriate for representation in XMPP IRIs or URIs.
   Care must also be taken in exposing XMPP addresses in the authority
   and path components of XMPP IRIs or URIs that are publicly
   accessible.

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

   Passwords and other user credentials are forbidden in the authority
   component (and in fact are not needed since the use of [SASL] in XMPP
   makes it possible to use the SASL ANONYMOUS mechanism if desired).

6.  References

6.1  Normative References

   [ABNF]     Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 2234, November 1997.

   [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.



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   [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.

   [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.

   [IMP-MODEL]
              Day, M., Rosenberg, J., and H. Sugano, "A Model for
              Presence and Instant Messaging", RFC 2778, February 2000.

   [IMP-REQS]
              Day, M., Aggarwal, S., and J. Vincent, "Instant Messaging
              / Presence Protocol Requirements", RFC 2779,
              February 2000.

   [JEP-0009]
              Adams, D., "Jabber-RPC", JSF JEP 0009, December 2002.

   [JEP-0030]
              Hildebrand, J., Millard, P., Eatmon, R., and P. Saint-
              Andre, "Service Discovery", JSF JEP 0030, March 2005.

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

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



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

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

   [JEP-0077]
              Saint-Andre, P., "In-Band Registration", JSF JEP 0077,
              July 2005.

   [JEP-0147]
              Saint-Andre, P., "XMPP IRI/URI Query Components", JSF
              JEP 0147, September 2005.

   [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.

   [NAMEPREP]
              Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
              Profile for Internationalized Domain Names (IDN)",
              RFC 3491, March 2003.

   [SASL]     Myers, J., "Simple Authentication and Security Layer
              (SASL)", RFC 2222, October 1997.

   [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/).

   [URL-GUIDE]



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              Masinter, L., Alvestrand, H., Zigmond, D., and R. Petke,
              "Guidelines for new URL Schemes", RFC 2718, November 1999.

   [URL-REG]  Petke, R. and I. King, "Registration Procedures for URL
              Scheme Names", BCP 35, RFC 2717, November 1999.

   [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: stpeter@jabber.org


























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