XEP-0328: JID Preparation and Validation Service

1. Introduction¶

To accurately compare and match JIDs, a normalization step is required by RFC 7622 [1]. This normalization is split into two steps called 'Preparation' and 'Enforcement' by RFC 8264 [2] 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.

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.

2. Discovering support¶

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 Service Discovery (XEP-0030) [3].

<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>

3. Use Cases¶

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 <jid-validate-request/> element qualified by the 'urn:xmpp:jidprep:1' namespace. This element contains a <maybe-jid/> child element whose textual content is the string to normalize to and validate as JID.

<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>

If the given string can be enforced to a valid JID, then a <jid-validate-result/> with a <valid-jid/> child element is returned. This child element contains the normalized JID parts. The valid-jid element MUST contain <domainpart/> and may contain <localpart/> and/or <resourcepart/> 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.

<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>

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

<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>

<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>

4. Optional Base64 Encoding¶

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 (RFC 4648 [4] § 4) and places the result into an <base64-maybe-jid/> element. This element is a put under the <jid-validate-base64-request/> IQ child element qualified by the 'urn:xmpp:jidprep:1' namespace.

The IQ respones of the service are identical to the ones of the non-Base64 case.

If supported, service announces 'urn:xmpp:jidprep:base64:1' feature.

<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>

5. Implementation Notes¶

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

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

6. Security Considerations¶

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.

7. IANA Considerations¶

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [5].

8. XMPP Registrar Considerations¶

9. XML Schema¶

TODO: Add once the XEP leaves the experimental state.

Appendices

Appendix A: Document Information¶

Series

XEP

Number

0328

Publisher

XMPP Standards Foundation

Status

Deferred

Type

Standards Track

Version

0.2.1

Last Updated

2019-12-16

Approving Body

XMPP Council

Dependencies

XMPP Core, XMPP IM, XEP-0030

Supersedes

None

Superseded By

None

Short Name

jid-prep

Source Control

HTML

This document in other formats: XML  PDF

Appendix B: Author Information¶

Lance Stout

Email

lance@lance.im

JabberID

lance@lance.im

Florian Schmaus

Email

flo@geekplace.eu

JabberID

flo@geekplace.eu

Appendix C: Legal Notices¶

Appendix D: Relation to XMPP¶

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.

Appendix E: Discussion Venue¶

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Discussion on other xmpp.org discussion lists might also be appropriate; see <https://xmpp.org/community/> for a complete list.

Errata can be sent to <editor@xmpp.org>.

Appendix F: Requirements Conformance¶

The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".

Appendix G: Notes¶

Appendix H: Revision History¶

Note: Older versions of this specification might be available at https://xmpp.org/extensions/attic/

1. Version 0.2.1 (2019-12-16)¶

   Typographical fix.

   nv
2. Version 0.2 (2019-09-09)¶
   • 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.
   • Return the normalized JID in its parts, to make it clear which parts constitute the JID
   • 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.
   • Add support for base64 encoding.
   • Always announce the jidprep identity.
   fs
3. Version 0.1 (2013-05-28)¶

   Initial published version approved by the XMPP Council.

   psa
4. Version 0.0.2 (2013-05-21)¶

   Incorporated feedback.

   lance
5. Version 0.0.1 (2013-05-08)¶

   Initial version.

   lance

Appendix I: Bib(La)TeX Entry

@report{stout2013jid-prep,
  title = {JID Preparation and Validation Service},
  author = {Stout, Lance and Schmaus, Florian},
  type = {XEP},
  number = {0328},
  version = {0.2.1},
  institution = {XMPP Standards Foundation},
  url = {https://xmpp.org/extensions/xep-0328.html},
  date = {2013-05-08/2019-12-16},
}

END