xeps/xep-0328.xml

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<!DOCTYPE xep SYSTEM 'xep.dtd' [
  <!ENTITY % ents SYSTEM 'xep.ent'>
%ents;
]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
<header>
  <title>JID Preparation and Validation Service</title>
  <abstract>This specification defines a way for an XMPP entity to request another entity to prepare and validate a given JID.</abstract>
  &LEGALNOTICE;
  <number>0328</number>
  <status>Deferred</status>
  <type>Standards Track</type>
  <sig>Standards</sig>
  <dependencies>
    <spec>XMPP Core</spec>
    <spec>XMPP IM</spec>
    <spec>XEP-0030</spec>
  </dependencies>
  <supersedes/>
  <supersededby/>
  <shortname>jid-prep</shortname>
  <author>
    <firstname>Lance</firstname>
    <surname>Stout</surname>
    <email>lance@lance.im</email>
    <jid>lance@lance.im</jid>
  </author>
  &flow;
  <revision>
    <version>0.2.1</version>
    <date>2019-12-16</date>
    <initials>nv</initials>
    <remark><p>Typographical fix.</p></remark>
  </revision>
  <revision>
    <version>0.2</version>
    <date>2019-09-09</date>
    <initials>fs</initials>
    <remark>
      <ul>
        <li>Do not return error IQ result if the string to validate is
        not a valid JID. It is indistinguishable if the error is
        caused by the string to check, or if some other involved JID,
        like the one in the 'to' attribute, is malformed.</li>
        <li>Return the normalized JID in its parts, to make it clear
        which parts constitute the JID</li>
        <li>Do not use text as child of an IQ child element. Using
        text makes it impossible to inject further child elements as
        XMPP disallows mixed content.</li>
        <li>Add support for base64 encoding.</li>
        <li>Always announce the jidprep identity.</li>
      </ul>
    </remark>
  </revision>
  <revision>
    <version>0.1</version>
    <date>2013-05-28</date>
    <initials>psa</initials>
    <remark><p>Initial published version approved by the XMPP Council.</p></remark>
  </revision>
  <revision>
    <version>0.0.2</version>
    <date>2013-05-21</date>
    <initials>lance</initials>
    <remark><p>Incorporated feedback.</p></remark>
  </revision>
  <revision>
    <version>0.0.1</version>
    <date>2013-05-08</date>
    <initials>lance</initials>
    <remark><p>Initial version.</p></remark>
  </revision>
</header>

<section1 topic='Introduction' anchor='intro'>

  <p>To accurately compare and match JIDs, a normalization step is
  required by &rfc7622;. This normalization is split into two steps
  called 'Preparation' and 'Enforcement' by &rfc8264; and maybe
  resource-intensive. The protocol defined herein, called "JID Prep"
  can be used to ask XMPP entities to perform such a
  normalization. Amongst other use-cases, this protocol can be used
  for testing purposes, where a test suite checks the conformance of
  an normalization implementation of, e.g., an XMPP server
  implementation.</p>

  <p>Furthermore, in some environments, especially ones like IoT where
  devices with constraint resources are used, a client may not have
  access to the various Unicode and internationalization libraries
  necessary to properly normalize a JID. For those situations, this
  protocol can be used by a client to ask a server to normalize a JID
  on its behalf.</p>

</section1>

<section1 topic='Discovering support' anchor='disco'>

  <p>If a server supports JID Prep queries, it MUST specify the
  'urn:xmpp:jidprep:1' feature in its service discovery information
  features as specified in &xep0030;.</p>

  <example caption='Server advertises support for JID prep queries'><![CDATA[
<iq type="result"
    to="juliet@capulet.lit/balcony"
    from="capulet.lit"
    id="info1">
  <query xmlns="http://jabber.org/protocol/disco#info">
    <identity category="component" type="jidprep" />
    ...
    <feature var="urn:xmpp:jidprep:1" />
  </query>
</iq>]]></example>

</section1>

<section1 topic='Use Cases' anchor='usecases'>

  <p>To request preparation and enforcement, and thus normalization
  and validation, of a string to a JID, the client sends a JID Prep
  request to the service. This request is an &IQ; of type 'get',
  containing a &lt;jid-validate-request/&gt; element qualified by the
  'urn:xmpp:jidprep:1' namespace. This element contains a
  &lt;maybe-jid/&gt; child element whose textual content is the string
  to normalize to and validate as JID.</p>

  <example caption='JID prep request (valid JID)'><![CDATA[
<iq type='get'
    from='user@example.org/resource'
    to='example.org'
    id='request1'>
  <jid-validate-request xmlns='urn:xmpp:jidprep:1'>
    <maybe-jid>Σ@example.com/resource</maybe-jid>
  </jid-validate-request>
</iq>]]></example>

    <p>If the given string can be enforced to a valid JID, then a
    &lt;jid-validate-result/&gt; with a &lt;valid-jid/&gt; child
    element is returned. This child element contains the normalized
    JID parts. The valid-jid element MUST contain &lt;domainpart/&gt;
    and may contain &lt;localpart/&gt; and/or &lt;resourcepart/&gt;
    elements. If the JID does not contain a local- or resourcepart,
    then the corresponding element is omitted. Those elements contain the
    normalized, i.e., PRECIS enforced, strings of the own JID
    parts.</p>

  <example caption='Valid JID result'><![CDATA[
<iq type='result'
    from='example.org'
    to='user@example.org/resource'
    id='request1'>
  <jid-validate-result xmlns='urn:xmpp:jidprep:1'>
    <valid-jid>
      <localpart>σ</localpart>
      <domainpart>example.com</domainpart>
      <resourcepart>resource</resourcepart>
    <valid-jid>
  </jid-validate-result>
</iq>]]></example>

  <p>If the service is given an invalid JID, a
  &lt;jid-validate-result/&gt; IQ result response with an
  &lt;invalid-jid/&gt; elmeent is returned.</p>

  <example caption='JID Prep request (invalid JID)'><![CDATA[
<iq type='get'
    from='user@example.org/resource'
    to='example.org'
    id='request2'>
  <jid-validate-request xmlns='urn:xmpp:jidprep:1'>
    <maybe-jid>henryⅣ@example.com</maybe-jid>
  </jid-validate-request>
</iq>]]></example>

  <example caption='Invalid JID result'><![CDATA[
<iq type='result'
    from='example.org'
    to='user@example.org/resource'
    id='request2'>
  <jid-validate-result xmlns='urn:xmpp:jidprep:1'>
    <invalid-jid>
      <reason>Invalid codepoint 'Ⅳ' in localpart.</reason>
    </invalid-jid>
  </jid-validate-result>
</iq>]]></example>

</section1>

<section1 topic='Optional Base64 Encoding' anchor='base64'>

  <p>To be able to feed arbitrary strings into the validator, not
  being limited by XML 1.0, the protocol supports an optional Base64
  encoding of the string to validate. The requestor first encodes the
  string to UTF-8, then encodes the UTF-8 byte-sequence using Base64
  (&rfc4648; <link
  url='https://tools.ietf.org/html/rfc4648#section-4'>§ 4</link>) and
  places the result into an &lt;base64-maybe-jid/&gt; element. This
  element is a put under the &lt;jid-validate-base64-request/&gt; IQ
  child element qualified by the 'urn:xmpp:jidprep:1' namespace.</p>

  <p>The IQ respones of the service are identical to the ones of the
  non-Base64 case.</p>

  <p>If supported, service announces 'urn:xmpp:jidprep:base64:1'
  feature.</p>

    <example caption='JID Prep request using Base64'><![CDATA[
<iq type='get'
    from='user@example.org/resource'
    to='example.org'
    id='request1'>
  <jid-validate-base64-request xmlns='urn:xmpp:jidprep:1'>
    <base64-maybe-jid>zqNAZXhhbXBsZS5jb20vcmVzb3VyY2U=</base64-maybe-jid>
  </jid-validate-base64-request>
</iq>]]></example>

</section1>

<section1 topic="Implementation Notes" anchor='impl'>

  <p>If a client has the ability to perform the normalization process
  itself, it SHOULD NOT make use of the protocol defined herein.</p>

  <p>Upon a successful response, it is RECOMMENDED that the client
  caches the result, mapping the original JID to the normalized
  version.</p>

</section1>

<section1 topic='Security Considerations' anchor='security'>

  <p>As the process for normalizing and validating a JID can be
  resource intensive, there is a possibility for denial of service
  attacks. A server MAY rate limit the number of requests to prevent
  such attacks. Likewise, the server MAY restrict access to the
  service torequests from users that are local to the server or
  otherwhise trusted.</p>

</section1>

<section1 topic='IANA Considerations' anchor='iana'>
  <p>This document requires no interaction with &IANA;.</p>
</section1>

<section1 topic='XMPP Registrar Considerations' anchor='registrar'>

  <section2 topic='Protocol Namespaces' anchor='ns'>

    <p>The &REGISTRAR; includes 'urn:xmpp:jidprep:1' in its registry of protocol namespaces (see &NAMESPACES;).</p>

    <ul>
      <li>urn:xmpp:jidprep:1</li>
    </ul>

  </section2>

  <section2 topic='Protocol Versioning' anchor='registrar-versioning'>
    &NSVER;
  </section2>

</section1>

<section1 topic='XML Schema' anchor='schema'>

  <p>TODO: Add once the XEP leaves the experimental state.</p>

</section1>

</xep>